DEV Community: Abel Lifaefi Mbula

chalk equivalent in Flask

Abel Lifaefi Mbula — Thu, 08 Sep 2022 13:13:29 +0000

Hello!

If you work in JS Nodejs world, you know that we have a npm called chalk that is used to "colorify" the terminal. I'm wondering if there is a pip. Do share with me if you happen to know one.

Bubble sort explained to a 6-year-old kid

Abel Lifaefi Mbula — Fri, 14 Jan 2022 06:31:25 +0000

You're a programmer, right? But do you rally think like programmers (or computer scientists) do?

When going for job interviews, you're likely to meet data structure and algorithm questions. This helps companies make sure they hire a systematic problem solver developer.

In this shot, I want you to learn more about one of the simplest sorting algorithms out there: bubble sort. How it works and how do we implement it with Java language.

The bubble sort in a nutshell

There we are: what is bubble sort?

Bubble sort is one type of sorting algorithms, and the simplest one, which is used to repeatedly compare adjacent items in a list and exchange them if they are in wrong order.

Let consider a list that need to be sorted in ascending order. To do this with bubble sort, we will start by comparing the first item of the list with the second one, if the first item is greater than the second, we swap both items, and then move on to compare the second and the third items, and so on. So, for a given list of size n, we need to repeat this process n - 1 times.

Note:

bubble sort is also called comparison alogorithm

In real life, we can observe bubble sort when people in a queue wanting to be standing in a high wise sorted manner swap their positions among themselves until everyone is standing based on increasing order of heights

Let's visualize an example of bubble sort so that you get it very well.

Bubble sort in practice

Here, I'll explain with an example how the bubble sort works, then after we will implement the algorithm in Java.

Let's consider this list of integer values: 19, 1, 9, 3, 10, 13. We want it to be sorted in ascending order.

We can now proceed with the comparison. You can notice that I've added indexes above each item of the list.

First iteration

We start with the first and second item: 19 > 1 is true, so we need to swap both items.

Our list looks now like this:

Next, we compare the second item with the third one: 19 > 9 is true, again we need to swap.

The new list is formed as follows:

We proceed with the third and fourth items: 19 > 3 is true, we swap as before.

Again, our list is arranged like this:

Let's continue the comparison with the fourth and the fifth items: 19 > 10 is true, once more we swap.

After swapping, the list is now as follows

We proceed with the fifth item and the last one: 19 > 13 is true, we need to swap.

Thus, after swapping item 5 and item 6, the list becomes:

This is the end of the first iteration. Notice how the largest item (19) is at the last position. 10 and 13 are also at their position.

Second iteration

We will be doing the same thing as in the first iteration.

We proceed with the first and the second items: 1 > 9 is false, so no swapping.

Next, we proceed with 9 and 3: 9 > 3 is true, we swap.

After swapping, the list is now like this:

Every item is in its right position. This marks the end of the process.

Note: If the list was not yet sorted as expected, we could continue with the third, nth processes until we get a fully sorted list.

Bubble sort: Pseudocode

It's always a good practice to use pseudocode before actual implementation. This is one for the bubble sort.

function bubbleSort(arr)
Set isSwapped to true
WHILE isSwapped = true
    Reset isSwapped to false
    FOR each item in the arr
        IF current item > next item
            swap items
            Reset isSwapped to true
        ENDIF
    ENDFOR
ENDWHILE
RETURN arr

Bubble sort: Java implementation

Now is the time to implement the algorithm. We are using Java here. If you want a JavaScript implementation, use this link.

We create two classes:

BubbleSort.java for the implementation of the logic
Main.java to test the implementation

BubbleSort.java

Let's create a method called sort() and implement the first iteration.

public class BubbleSort {
    public void sort(int[] list) {
        for (int i = 0; i < list.length - 1; i++) {
            if(list[i] > list[i + 1]) {
                // swap is true
                int temp = list[i];
                list[i] = list[i + 1];
                list[i + 1] = temp;
            }
        }
    }

}

Our method is not that complicated. We're going through the list of integers by comparing adjacent items to see if they need to be swapped. If so, we do swap them. Look how we've implemented our swapping system:

first, we keep the left item in temporary variable, temp
next, we assign the value of the right item to the left one
last, the right item is assigned temp

To make our code cleaner and more readable, let's move the swap logic into a method called swap().

private void swap(int[] list, int curr_index) {
  int temp = list[curr_index];
  list[curr_index] = list[curr_index + 1];
  list[curr_index + 1] = temp;
}

Our is working pretty fine, but only for one iteration, which is not enough to sort the list as expected.

Let's modify the code so that it can loop over and over until we get a fully sorted list.

public class BubbleSort {
    public void sort(int[] list) {
        boolean isSwapped = true;

        while (isSwapped) {
            isSwapped = false;
            for (int i = 0; i < list.length - 1; i++) {
                if(list[i] > list[i + 1]) {
                    isSwapped = true;
                    swap(list[i], list[i + 1]);
                }
            }
        }
    }

    private void swap(int left_item, int right_item) {
        int temp = left_item;
        left_item = right_item;
        right_item = temp;
    }

}

What did we do here? We've created a boolean variable, isSwapped and initialized to true so that we can use it in a while loop. Inside the while loop, we first assume that we want need swapping, so we set isSwapped to false. If we end up swapping, we reset it back to true.

We can now test our implementation.

Main.java

public class BubbleSort {
    public void sort(int[] list) {
        boolean isSwapped = true;

        while (isSwapped) {
            isSwapped = false;
            for (int i = 0; i < list.length - 1; i++) {
                if(list[i] > list[i + 1]) {
                    swap(list, i);
                    isSwapped = true;
                }
            }
        }
    }

    private void swap(int[] list, int curr_index) {
          int temp = list[curr_index];
          list[curr_index] = list[curr_index + 1];
          list[curr_index + 1] = temp;
    }

}

Congratulations! You've been able to implement Bubble sort algorithm in Java.

One more thing for your information: complexity of the algorithm

Complexity analysis

To end our journey, let me say just one word about the performance of this algorithm.

Bubble sort is a very simple sorting algorithm and also the very slow one. For this reason, you'll almost never find or use it in the real world. In fact, it is mostly used for educational purposes.

Worst Case Time Complexity, aka Big-O: $O(n^2)$
Best Case Time Complexity, aka Big-omega: $O(n)$
Average Time Complexity, aka Big-theta: $O(n^2)$
Space Complexity: $O(1)$

Happy coding!

How to get a user’s LinkedIn account, Twitter username, and more from a single line of code

Abel Lifaefi Mbula — Fri, 29 Oct 2021 20:35:32 +0000

Users' data is the gold for your business. But, how do you know more about your users when you only have or collect a piece of information like phone numbers or emails?

We are living in a digital age where people are more connected than ever before and almost everyone is on social media like Twitter or LinkedIn. One way to know more about your users is to go on the social media they are. But, this will only help if you have a tiny number of users because you have to

Try whether they are on Twitter or LinkedIn or another social media
Manually go on the user social media account to have information

This is not productive for your business, and you shouldn’t even try it. There need to be something better to help you. Like gold, the quality of data is also important.

Looking around, we could not find a suitable solution that could help us enough, just like you. So, we developed one, and we call it Kelvin Data. Kelvin Data can be used by developers through an API (GraphQL or RESTful) or by anyone through a web portal.

Your business is so important to us, so we have designed Kelvin Data with that in mind. We focus on structuring and organizing data from around the web to make it accessible and easy-to-use so that you have a ready to use data set while still continuing running your business.

Let’s take a deep dive here to see how to use Kelvin Data to better know your users.

Kelvin Data 101

No matter what your site or app does, knowing more about your users gives you more opportunities. Let’s see some of them:

You can easily fight fraud
Send email based on their location
Increase your sale power
And more

Thanks to Kelvin Data, you can achieve your goal with easy, no matter what it is. Here is how it works.

First, you need an API key for authentication with us. You can find one here. Now that you have a valid key, you can make a call to our API by providing us with at least one piece of information you have for your user, like email or phone number.

Let’s consider an example. Your user email is jared@ycombinator.com. The API endpoint you’ll call looks like this:

https://api.kelvindata.com/rest/v1/search-v2?email=jared@ycombinator.com&apiKey=your-apikey-here

And this is the result you’ll have (I’m using the web portal here).

Kelvin Data is a powerful and simple platform whose mission is to structure and organize data from around the web to make it accessible and easy-to-use. We offer flexible pricing plans to meet your business needs. Sign up to get started, or contact us to learn more.

How to Setup a Minimal Node.js Server

Abel Lifaefi Mbula — Fri, 14 May 2021 11:03:19 +0000

Node.js is a JavaScript engine that let us use JS language in the backend. You can say goodbye to Apache, Ngix servers or something similar for your backend needs. Thanks to Node.js, your JS knowledge is enough to work in the backend.

TL;DR–Explore the example repository

Goals

bootstrap a Node.js server
serve up an HTML file

Prerequisites

have Node.js installed in your local machine (at least version 10)
have a basic knowledge of CLI (command-line interface)

To check your Node.js installation, open your terminal and type

node --version

mine is v14.4.0

Check also the packet manager that comes with Node.js npm

npm --version

mine is 6.14.7

In case you don't have Node.js, go here to download it.

The project initialization

We need a folder to locate our project. Create one and name it as you want and move to it. In this tutorial, I'm using the CLI.

mkdir node-server
cd node-server

The folder name is node-server.

Once in our project folder, from the CLI, we can now initialize the npm project like this:

npm init -y

Nothing tricky here, we're initializing an npm project with default values (-y flag). If you leave -y flag you'll be answering questions interactively. Maybe you should try it :).

Did you notice it? npm has created a file (ls to see it) called:

package.json

package.json is an important file in any Node.js project as it keeps all info (values) for the projet: author, licence, packages...

If you want to see defaults info in package.json, use this command:

npm config list

In case you want to change defaults, use npm set <key><value>

npm set init.author.name "<Your Name>"
npm set init.author.email "you@example.com"
npm set init.author.url "example.com"
npm set init.license "MIT"

There's much to say about the package.json file, but I think we can stop by there for now.

Now is the time to discuss the file organization.

The file structure

There are many file organizations out there. You should feel free to go with one that works fine for you. In this section, I'm showing you one of the ways I do.

Make sure you're in our initial project folder (node-server). From there create an src folder and within it create server.js and app.js and views and public.

mkdir src && cd src
touch server.js app.js
mkdir views public

I find it better to separate API declarations (app.js) from network concerns (server.js), but I see many friends using just one file either server.js or app.js. The views folder is about the screen (html files or template like pug). In public folder I put images, styles and scripts.

In final, my file structure looks like this

Now, we can start coding.

Bootstrapping a Node.js server with Express.js

To create a Node.js server, it's easy and recommended to use a framework like Express.js. To add a JS package as a dependency in your project, you use this syntax: npm install --save <package name>.

Let's install Express.js package.

npm install --save express

If the installation is successful, you'll see a node_modules folder created in your project directory. Also, in the package.json under dependencies property express is added with its version ("express": "^4.17.1").

Note:

If you're using git, do add node_modules in .gitignore.

We can now make use of express.

Go to app.js and add this code:

// app.js
const express = require("express")

const app = express()

module.exports = app

Nothing tricky here. We require express, we create an instance of it so that we can use it in the project and at the end we export the file.

We can now start the server in server.js

const app = require("./app")
const port = 4000

app.listen(port, () => console.log(`The server is listening on port ${port}`))

We use app.listen() function that binds and listens the connections on the specified host and port. To see if everything is OK we can start the server like this:

node src/server.js

You should get this message on the console The server is listening on port 4000. But if you go on localhost:4000 you'll get an error (Cannot GET /) because we did not define any route yet. We can add a simple route like this:

// app.js
// previous code here...

app.get("/", (req, res) => {
  res.send("Hello")
})

For productivity purposes, we can add color to our console messages and a logger to get the log on the console. Install these packages:

npm install chalk morgan

Once done, we can configure them like this:

// server.js
const color = require("chalk")

app.listen(port, () =>
  console.log(`The server is listning on port ${color.green(port)}`)
)

I'm using chalk green color here. You can use the one you want. Check the doc!

// app.js
const logger = require("morgan")

app.use(logger("tiny"))

morgan is a logger middleware. You can log anything you want on the console. You can log as much info as you want. Here I only want some basic info, so I use tiny. Other options are combined, dev, common, short. Try them yourself and see the output or read the doc.

Run the server (node src/server.js) and see the result. On the browser you have Hello, on the console 4000 is in green color and some other info printed there.

Just one more thing before we jump to serving up an html file. Instead of typing everytime node src/server.js, we can add it to our package.json so that we can use the automated tools out there like npm start. So, under scripts property add

"start": "node src/server.js"

Even better, add src/server.js as the value of main property and modify the "start" script like so:

"start": "node ."

To start the server, you simply have to do npm start.

To finish this section, add the string "world" after after "Hello" and go to the browser to see the result. Do you see "world"? No, sorry :(. The reason is that, the server did not restart to serve up new modifications. Stop the server (Ctrl + C) and restart it. Now you can see "Hello world" on the browser.

To allow the automatic restart of the server, we can use nodemon package. Install it and modify the "start" script as so: "start": "nodemon .".

Congratulations! Your server is up and listening fine on port 4000.

Now is the time to serve up HTML file.

Serving files

In the views forlder, create a file called index.html and add this content:

<!--views/index.html-->
<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>Node.js Starter</title>
  </head>
  <body>
    <h1>Hello!</h1>
    <p>If you can see this text, your server is running properly.</p>
  </body>
</html>

How can we see the content of the file above on the browser?

Let's learn how to:

Deal with files and directories

To work with files and directories in a Node.js app, we need these elements:

sendFile(): an Express.js method available on the response object (res) that is used to render a file
path: a buit-in module that gives us all of the tools we need to handle cross-platform paths.
__dirname: a global object that return the absolute path of the directory containing the currently executing file

Let's put all into practice.

res.sendFile(path);

The path we want want send is this views/index.html. We could just do this to define our path:

res.sendFile(__dirname + "views/index.html");

The code above will just work fine if you are on a UNIX-like system. If you're developing in a Windows machine you'll encounter some problems as paths do not work the same on Windows OS and MacOSX or GNU/Linux. To avoid having troubles, we can let Node.js handle this for us. Welcome path module!

// app.js
const path = require("path");

app.get("/", (req, res) => {
  res.sendFile(path.join(__dirname, "views", "index.html"));
});

I include the path module in the project and use its .join() method to join (concatenate) all paths into a string. The final path after I run the server will look like this:

/home/abelmbula/Documents/dev/educative-courses/node-starter/src/views/index.html

Wrap up

In this lesson, we learned how to create a simple Node.js server with Express framework and how to render an html file. You can find the full code here.

The 15 Algorithm Challenges I Solved in May 2020

Abel Lifaefi Mbula — Fri, 30 Apr 2021 11:04:33 +0000

I don't know you, but it seems to me that the year is flying away too fast. I'm looking for a remote position this year, so I've decided to work too hard: build tools, write blog posts, help people in forums, and of course work on data structure and algorithms.

Last month, May 2020, I did work on around 15 challenges on FreecodeCamp and LeetCode. Let's take a look at them. I'll try to add some explanations, if necessary. The language I'm using to solve all these challenges is JavaScript.

Let's get started!

-1- Sum All Numbers in a Range

The link to the challenge is here.

The Challenge Description

We'll pass you an array of two numbers. Return the sum of those two numbers plus the sum of all the numbers between them. The lowest number will not always come first.
For example, sumAll([4,1]) should return 10 because sum of all the numbers between 1 and 4 (both inclusive) is 10.

My Solution

function sumAll(arr) {
  /*
   * 1. Let's sort the array to ensure that we have:
   * - small value on the left and
   * - big number on the right
   * E.g. [4, 1] => [1, 4]
   */
  arr.sort((a, b) => a - b)

  let res = arr[0] + arr[1] // 2. Set res with the sum of the 2 values in the array (1 + 4)

  // 3. Iterate over the second value of the array (4)
  for (let i = arr[0] + 1; i < arr[1]; i += 1) {
    res += i // 4. add the current value to res
  }
  return res // 5. return res
}

sumAll([1, 4])

If you run the test with this code, you'll get 100% tests pass.

Let's another way to resolve this challenge.

Alternative Solution and Improvement

The solution above is the way I did when working on that algorithm challenge. But there are many other ways to do so. And you can also improve my code to make it robust.

Let's see how.

Improvement

Although our code seems to works properly in the context of this challenge, it has some weaknesses. Let's find them.

Our code only assumes that the user will always submit the right argument when this is not true in the real world.

What happens if the user calls the function without any argument at all?
What if the argument is not an array?
What if the array contains more than 2 values or it contains a mix of string and numbers?

We should handle all these situations. In programming, there's a saying that says never trust user input.

First thing first, the requirements for our function to run properly:

the parameter must exist
it must be an array
the array should only contain 2 numbers

Then the implementation:

if (!arr) return "The parametor is required and must not be empty"
if (!Array.isArray(arr)) return "The parametor must be an array"
if (arr.length != 2) return "The array must be of length 2"

Putting all together, we get this

function sumAll(arr) {
  if (
    arr &&
    Array.isArray(arr) &&
    arr.length == 2 &&
    typeof arr[0] == "number" &&
    typeof arr[1] == "number"
  ) {
    arr.sort((a, b) => a - b)
    let res = arr[0] + arr[1]

    for (let i = arr[0] + 1; i < arr[1]; i += 1) {
      res += i
    }
    return res
  } else {
    return "There'se something wrong with your argument. Please check it and try again"
  }
}

sumAll([1, 4])

Here we start by checking the validity of the argument sent by the user. If something is wrong, the function can't proceed and tells the user to check for the argument.

Alternative Solutions

The solution above is the way I did when I was working on the challenge. But I can see another way to do it and you've got another too.

Here's the idea.

generate all array items in the range of first value - second value. E.g.: [1, 4] => [1, 2, 3, 4].
get the sum by using reduce() method.

Let's implement the idea above.

function sumAll(arr) {
 if(/*check arr validity here*/){
    arr.sort((a,b) => a - b)

    const newArr = [] // create a new arr

    for(let i = arr[0]; i <= arr[1]; i += 1) newArr.push(i) // add items to the new arr

    return newArr.reduce((acc, cur) => acc + cur)
 } else {
     return 'There\'se something wrong with your argument. Please check it and try again'
 }
}

Resource(s)

Link to the challenge, FreeCodeCamp
reduce() method, MDN web docs
Array.isArray() method, MDN web docs

-2- Slice and Splice

Link

You are given two arrays and an index.
Use the array methods slice and splice to copy each element of the first array into the second array, in order.
Begin inserting elements at index n of the second array.
Return the resulting array. The input arrays should remain the same after the function runs.
function frankenSplice(arr1, arr2, n) {
  return arr2
}
frankenSplice([1, 2, 3], [4, 5, 6], 1)

Resources

slice() method, MDN web docs
splice() method, MDN web docs

-3- Confirm the Ending

I've written a detailed post about this here. No time? Read below.

Let's first take the challenge description.

Check if a string (first argument, str) ends with the given target string (second argument, target).
This challenge can be solved with the .endsWith() method, which was introduced in ES2015. But for the purpose of this challenge, we would like you to use one of the JavaScript substring methods instead.
function confirmEnding(str, target) {
  return str
}
confirmEnding("Bastian", "n")

And here's the final solution.

function confirmEnding(str, target) {
  const newStr = str.split(" ").join("")
  const strL = newStr.length
  const targetL = target.length
  const targetIdx = strL - targetL
  const subStr = newStr.substring(targetIdx)

  return subStr == target
}

confirmEnding("I am a test", "st")

-4- Repeat a String

This challenge is available following this link. It is stated as this:

Repeat a given string str (first argument) for num times (second argument). Return an empty string if num is not a positive number.
function repeatStringNumTimes(str, num) {
  return str
}

repeatStringNumTimes("abc", 3)

My solution is

function repeatStringNumTimes(str, num) {
  let repeatedStr = ""

  if (num < 0) return repeatedStr

  for (let i = 0; i < num; i += 1) repeatedStr += str

  return repeatedStr
}

-5- Finders Keepers

Click here to go to the challenge.

Create a function that looks through an array (first argument) and returns the first element in the array that passes a truth test (second argument). If no element passes the test, return undefined.
function findElement(arr, func) {
  let num = 0
  return num
}
findElement([1, 2, 3, 4], num => num % 2 === 0)

Here's how I did solve it:

function findElement(arr, func) {
  let num = 0
  // Solution 1 with for loop
  for (let i = 0; i < arr.length; i += 1) {
    if (func(arr[i]) === true) {
      num = arr[i]
      break
    } else num = undefined
  }
  // Solution 2 with forEach
  /*arr.forEach(elt => {
    if(func(elt) === true) num = elt
     else num = undefined
  })*/
  return num
}

As you can see, I use two solutions. One with traditional for loop and the second one with forEach

-6- Boo who

Link

Check if a value is classified as a boolean primitive. Return true or false.

Boolean primitives are true and false.
function booWho(bool) {
  return bool
}

booWho(null)

The Solution

function booWho(bool) {
  return bool === true || bool === false ? true : false
}

-7- Where do I Belong

Go to the challenge.

Return the lowest index at which a value (second argument) should be inserted into an array (first argument) once it has been sorted. The returned value should be a number.

For example, getIndexToIns([1,2,3,4], 1.5) should return 1 because it is greater than 1 (index 0), but less than 2 (index 1).

Likewise, getIndexToIns([20,3,5], 19) should return 2 because once the array has been sorted it will look like [3,5,20] and 19 is less than 20 (index 2) and greater than 5 (index 1).
function getIndexToIns(arr, num) {
  return num
}

getIndexToIns([40, 60], 50)

Solution

// Solution 1
function getIndexToIns(arr, num) {
  arr.push(num)
  arr.sort((a, b) => a - b)

  for (let i = 0; i < arr.length; i += 1) {
    if (arr[i] === num) return i
  }
}

// Solution 2
function getIndexToIns(arr, num) {
  const arrSort = arr.sort((a, b) => a - b)
  let index = 0

  for (let i = 0; i < arrSort.length; i += 1) {
    if (num < arrSort[i] || num == arrSort[i]) {
      index = i
      break
    } else {
      index = i + 1
    }
  }

  return index
}

Nothing tricky here. I first add the passed value to the array, then after I sort the array. The last step is to loop over the array and return the index of the value in the sorted array.

-8- Mutations

This challenge can be retrieved here.

Return true if the string in the first element of the array contains all of the letters of the string in the second element of the array.

For example, ["hello", "Hello"], should return true because all of the letters in the second string are present in the first, ignoring case.

The arguments ["hello", "hey"] should return false because the string "hello" does not contain a "y".

Lastly, ["Alien", "line"], should return true because all of the letters in "line" are present in "Alien".
function mutation(arr) {
  return arr
}

mutation(["hello", "hey"])

My solution is as follow:

function mutation(arr) {
  const baseStr = arr[0].toLowerCase()
  const targetStr = arr[1].toLowerCase()
  const targetL = targetStr.length

  for (let i = 0; i < targetL; i += 1) {
    if (!baseStr.includes(targetStr.charAt(i))) {
      return false
      break
    }
  }

  return true
}

-9- Title Case a Sentence

Challenge link

Return the provided string with the first letter of each word capitalized. Make sure the rest of the word is in lower case.

For the purpose of this exercise, you should also capitalize connecting words like "the" and "of".
function titleCase(str) {
  return str
}

titleCase("I'm a little tea pot")

Solution

function titleCase(str) {
  const words = str.toLowerCase().split(" ")
  const arrCap = []

  words.forEach(word => {
    arrCap.push(word.charAt(0).toUpperCase() + word.slice(1))
  })

  return arrCap.join(" ")
}

-10- Falsy Bouncer

Link

Here's how I solved it.

function bouncer(arr) {
  const falsyArr = [false, null, 0, "", undefined, NaN]
  const newArr = []

  arr.forEach(item => {
    if (!falsyArr.includes(item)) newArr.push(item)
  })
  return newArr
}

-11- Diff Two Arrays

Challenge link.

My solution

function diffArray(arr1, arr2) {
  var sumArr = [...arr1, ...arr2]
  const symArr = []

  sumArr.forEach(elt => {
    if (sumArr.indexOf(elt) == sumArr.lastIndexOf(elt)) {
      symArr.push(elt)
    }
  })

  return symArr
}

-12- Seek and Destroy

Go here to find the link.

My solution

function destroyer(arr) {
  const toDestroy = []
  const remainArr = []

  for (let i = 1; i < arguments.length; i++) {
    toDestroy.push(arguments[i])
  }

  arr.forEach(item => {
    if (!toDestroy.includes(item)) remainArr.push(item)
  })

  return remainArr
}

-13- Single Number

The challenge link.

Let's see the description.

Given a non-empty array of integers, every element appears twice except for one. Find that single one.

Note:

Your algorithm should have a linear runtime complexity. Could you implement it without using extra memory?

Example 1:
Input: [2,2,1]
Output: 1
Example 2:
Input: [4,1,2,1,2]
Output: 4

And now the solution

/**
 * @param {number[]} nums
 * @return {number}
 */
var singleNumber = function(nums) {
  const uniq = []
  nums.forEach(item => {
    if (nums.indexOf(item) == nums.lastIndexOf(item)) uniq.push(item)
  })

  return uniq
}

-14- Counting Bits

The link to the challenge is here if you need it.

The challenge description is as follows.

Given a non-negative integer number num. For every number i in the range 0 ≤ i ≤ num calculate the number of 1's in their binary representation and return them as an array.

Example 1:
Input: 2
Output: [0,1,1]
Example 2:
Input: 5
Output: [0,1,1,2,1,2]

Starter Code

/**
 * @param {number} num
 * @return {number[]}
 */
var countBits = function(num) {}

My Solution

var countBits = function(num) {
  const numArr = []
  const onesCountArr = []

  for (let i = 0; i <= num; i += 1) numArr.push(i)

  numArr.forEach(val => {
    const bin = val.toString(2)
    const OnesCount = (bin.match(/1/g) || []).length
    onesCountArr.push(OnesCount)
  })

  return onesCountArr
}

-15- K Closest Points to Origin

Visit the challenge site if you want.

We have a list of points on the plane. Find the K closest points to the origin (0, 0).

(Here, the distance between two points on a plane is the Euclidean distance.)

You may return the answer in any order. The answer is guaranteed to be unique (except for the order that it is in.)

Example 1:
Input: points = [[1,3],[-2,2]], K = 1
Output: [[-2,2]]

Explanation:
The distance between (1, 3) and the origin is sqrt(10).
The distance between (-2, 2) and the origin is sqrt(8).
Since sqrt(8) < sqrt(10), (-2, 2) is closer to the origin.
We only want the closest K = 1 points from the origin, so the answer is just [[-2,2]].
Example 2:
Input: points = [[3,3],[5,-1],[-2,4]], K = 2
Output: [[3,3],[-2,4]]
(The answer [[-2,4],[3,3]] would also be accepted.)
Note:
`

1 <= K <= points.length <= 10000

-10000 < points[i][0] < 10000

-10000 < points[i][1] < 10000

`

Starter Code

/**
 * @param {number[][]} points
 * @param {number} K
 * @return {number[][]}
 */
var kClosest = function(points, K) {}

Solution

var kClosest = function(points, K) {
  const result = []
  const distanceObjList = [] // store Euclidian distances here

  // find Euclidian distances
  points.forEach(arr => {
    let thisDistance = arr[0] * arr[0] + arr[1] * arr[1]
    distanceObjList.push({
      d: thisDistance,
      arr,
    })
  })

  distanceObjList.sort((x, y) => x.d - y.d)

  const subArr = distanceObjList.slice(0, K)

  subArr.forEach(arr => result.push(arr.arr))

  return result
}

That's all for now. Thank you for reading.

Share with me your solutions on Twitter.

My FLOSS Project is Launched! Come and Help!

Abel Lifaefi Mbula — Thu, 15 Apr 2021 12:34:50 +0000

Hey!

I've started a small project that aims at helping organizations easily manage their interns. The main idea is to manage interns' attendance, but we might add new features as requested.

The app is standalone that you can install on your local server or even computer.

The technical stack is Docker, PHP, MySQL...

Do use it and let me know things we can improve.

You can also contribute code as well.

The code is here.

How to Customize the Nano Text Editor in Linux

Abel Lifaefi Mbula — Thu, 14 Jan 2021 17:40:16 +0000

Think about making your Nano more enjoyable? This is a step by step guide on how to do so.

By default, Nano looks ugly and most people fear or can’t use it at all and prefer to go for Vi/Vim or Emacs. Truth be told, these editors have some really great features. But, do you know that with a little effort you can have most of their features in Nano?

Let’s see how.

In-line customization

First thing first. You need to try/preview the customization before setting it permanently. Don’t you?

So, how does it work? Very simple. You just need to add option(s) when calling Nano on your terminal as this:

As you can see in the image above, we will be opening the fizzbuzz.py file with the mouse support enabled on the command line. It means that mouse clicks can be used to place the cursor, set the mark (with a double click), and execute shortcuts. By default, the mouse is not supported on the console.

Note: mouse support is not available on a full command line system.

Some other options are: -i (autoindent), -l (display line numbers to the left of the text area)...

Need to see other available options? Type man nano on the terminal.

Are you satisfied with these preview customizations? Now is the time to

Permanently set customization rules with .nanorc

What’s .nanorc? It’s a file that contains configurations for… Nano. Nano reads it on startup. There’s one global file located at /etc/nanorc. But you can also create one for your own in your home (run cd ~ if not in home) that will overwrite global configurations.

Let’s now create our own nanorc.

From the CLI, run nano .nanorc and add as many rules as you can following the example below:

Save the file by doing Ctrl + X and hint Y (for yes).

Notes:

You can see that I’ve added a . (dot) before the name of the file, I do so to make the file hidden.

For more info about nanorc, type man nanorc

From now on, if you open Nano all your setups will be taken into account.

Enjoy your editing with Nano!

Let's discuss DBs

Abel Lifaefi Mbula — Wed, 13 Jan 2021 09:23:39 +0000

Hey Dev and happy new year 2021.

MySQL vs Postgress, what's your preference and why?

OAuth 2 Spec is misunderstood, why?

Abel Lifaefi Mbula — Thu, 13 Aug 2020 15:09:07 +0000

I'm writing a course on OAuth2 and OIDC. But I'm a bit sorry to see that when I search the web, most of the articles mislead users about OAuth. In most of them, they deal with OAuth as a way to authenticate. That is not correct, it is a misuse of this framework or standard. OAuth is short for open authorization.

Let's get the definition from the body authority, Internet Engineering Task Force (IETF):

enables a third-party application to obtain limited access to an HTTP service, either on behalf of a resource owner by orchestrating an approval interaction between the resource owner and the HTTP service or by allowing the third-party application to obtain access on its own behalf.

That's said, OAuth deals with delegated authorization nothing to have with authentification which consists of verifying if the user is what they claim they are.

I found a good post here on DEV that tries to explain well.

Authorization and Authentication For Everyone

Kim Maida ・ Jul 19 '20

#authorization #security #authentication #webdev

And you, did you also notice the misuse of OAuth? Share with us.

How to Add Bootstrap to your Nodejs Project

Abel Lifaefi Mbula — Mon, 10 Aug 2020 09:42:34 +0000

This article was originally published here in my blog.

If you're building apps with Nodejs and feel like you need a tool to help you enhance the UI, this article is for you. It will guide you step by step on how you can add Bootstrap to your Nodejs.

Let's create a simple app that contains the text Hello the World in a Bootstrap jumbotron.

The Initial Project

Create a simple Node project like the one below.

Nothing tricky here. Create a folder for your project and initialize it as Node project, npm init -y. Create the server file, app.js (touch app.js), and other directories (mkdir views).

Let's install express to configure a lightweight Node server.

npm i express or yarn add express.

We can now create our basic server.



const express = require("express")
const path = require('path')

const app = express();

app.get("/", (req, res) => {
  res.sendFile(path.join(__dirname, 'views/index.html'))
});

app.listen(5000, () => {
  console.log('Listening on port ' + 5000);
});

We are listening on port 5000 and serving up index.html file. Make sure you have it created already and add some html contents in it.

Start your server (node app.js) and see if everything is OK. If so, let's move to the next session.

Adding Bootstrap CSS

The first solution I'd suggest here is to use a CDN. Here's how you can do it.

Go here to copy Bootstrap CSS and eventually additional JS and paste them in your index file.

Using a CDN

Now is the time to modify our index.html so that we can add Bootstrap CSS.



<!doctype html>
<html lang="en">
  <head>
    <!-- Required meta tags -->
    <meta charset="utf-8">
    <meta name="viewport" content="width=device-width, initial-scale=1, shrink-to-fit=no">

    <!-- Bootstrap CSS -->
    <link rel="stylesheet" href="https://stackpath.bootstrapcdn.com/bootstrap/4.5.0/css/bootstrap.min.css" integrity="sha384-9aIt2nRpC12Uk9gS9baDl411NQApFmC26EwAOH8WgZl5MYYxFfc+NcPb1dKGj7Sk" crossorigin="anonymous">

    <title>Hello, the world!</title>
  </head>
  <body>
    <div class="jumbotron">
      <div class="container"><h1>Hello, the world!</h1></div>
    </div>

    <!-- Optional JavaScript -->
    <!-- jQuery first, then Popper.js, then Bootstrap JS -->
    <script src="https://code.jquery.com/jquery-3.5.1.slim.min.js" integrity="sha384-DfXdz2htPH0lsSSs5nCTpuj/zy4C+OGpamoFVy38MVBnE+IbbVYUew+OrCXaRkfj" crossorigin="anonymous"></script>
    <script src="https://cdn.jsdelivr.net/npm/popper.js@1.16.0/dist/umd/popper.min.js" integrity="sha384-Q6E9RHvbIyZFJoft+2mJbHaEWldlvI9IOYy5n3zV9zzTtmI3UksdQRVvoxMfooAo" crossorigin="anonymous"></script>
    <script src="https://stackpath.bootstrapcdn.com/bootstrap/4.5.0/js/bootstrap.min.js" integrity="sha384-OgVRvuATP1z7JjHLkuOU7Xw704+h835Lr+6QL9UvYjZE3Ipu6Tp75j7Bh/kR0JKI" crossorigin="anonymous"></script>
  </body>
</html>

I added two Bootstrap classes: container and jumbotron.

Restart your server and go check if Bootstrap is on the page (just see if a fluid jumbotron is there).

This solution is good, but when working offline, you'll be limited. That's why I want you to test the next solution.

Using `npm`

The first thing you have to do here is to install packages, which are bootstrap and optionally jquery.

npm i bootstrap jquery --save

To make use of these files we have to modify our app.js so that it will serve them to us.



// app.js
const express = require("express")
const path = require('path')

const app = express();

app.use('/css', express.static(path.join(_dirname, 'node_modules/bootstrap/dist/css')))
app.use('/js', express.static(path.join(_dirname, 'node_modules/bootstrap/dist/js')))
app.use('/js', express.static(path.join(_dirname, 'node_modules/jquery/dist')))

app.get("/", (req, res) => {
  res.sendFile(path.join(__dirname, 'views/index.html'))
});

app.listen(5000, () => {
  console.log('Listening on port ' + 5000);
});

Thanks to express.static() we are able to serve up Bootstrap without any difficulty.

Now we can make use of Bootstrap in our HTML pages by just linking to it as <link rel="stylesheet" href="./css/bootstrap.min.css">.

Conclusion

In this article, we learned how to integrate Bootstrap in our Nodejs project in two different ways. The first way is to use official CDN and the last one to use npm. This last solution is suitable if you're working locally (and offline).

Do you have another way to work with Bootstrap in a Node project? Share with us!

In case you like this post, consider hitting love and unicorn buttons or follow me on Twitter or read more post on my blog.

Five Ways to Solve the DNA Pairing Challenge in JavaScript

Abel Lifaefi Mbula — Tue, 14 Jul 2020 21:27:52 +0000

This article was first published here on my blog.

Computer Science is awesome and amazing, trust me! There is always more than one way to come to a solution to a given problem in most cases.

In this tutorial, we will learn how to solve the Free Code Camp DNA Pairing Challenge in five different ways.

The Challenge Description

The DNA strand is missing the pairing element. Take each character, get its pair, and return the results as a 2d array.
Base pairs are a pair of AT and CG. Match the missing element to the provided character.
Return the provided character as the first element in each array.
For example, for the input GCG, return [["G", "C"], ["C","G"],["G", "C"]]
The character and its pair are paired up in an array, and all the arrays are grouped into one encapsulating array.

function pairElement(str) {
  return str;
}

pairElement("GCG");

Provided Test Cases

pairElement("ATCGA") should return [["A","T"],["T","A"],["C","G"],["G","C"],["A","T"]]
pairElement("TTGAG") should return [["T","A"],["T","A"],["G","C"],["A","T"],["G","C"]]
pairElement("CTCTA") should return [["C","G"],["T","A"],["C","G"],["T","A"],["A","T"]]

Understanding the Problem

As you may have read in the challenge description above, the goal of this exercise is to return the missing trand into a 2d array.
In biology class, we learned about DNA base pairs (need a refresher? Wikipedia is your friend). They are A - T and C - G, and they go both ways. So every time we have:

A string we return an array ['A', 'T']
T string we return an array ['T', 'A']
C string we return an array ['C', 'G']
G string we return an array ['G', 'C']

1. Using For Loop, and If Statement

For this solution, we will loop over the parameter passed to the function and use if statement to return the correct pair.

function pairElement(str) {
  // Step 1. Declare the variable of type array that will encapsulate other paired arrays
  const arrDNA = [];

  // Step 2. Create the FOR loop with initializer less then str.length
  for (let i = 0; i < str.length; i += 1) {
    // Step 3. Use if statement to evaluate baise pair and push it to arrDNA
    if (str[i] === 'A') arrDNA.push([str[i], 'T']);
    if (str[i] === 'T') arrDNA.push([str[i], 'A']);
    if (str[i] === 'C') arrDNA.push([str[i], 'G']);
    if (str[i] === 'G') arrDNA.push([str[i], 'C']);
  }

  /* Here "GCG"'s length equals 3
      For each iteration: i = 0 and arrDNA = [[str[i], 'corresponding pair']]
      First iteration:  i = 0        arrDNA = [['G', 'C']]
      Second iteration: i = 1        arrDNA = [['G', 'C'], ['C', 'G']] 
      Third iteration:  i = 2        arrDNA = [['G', 'C'], ['C', 'G'], ['G', 'C']]         

    End of the FOR Loop*/

  // Step 4. Return the 2D array
  return arrDNA;
}

pairElement("GCG");

Without comments:

function pairElement(str) {

  const arrDNA = [];

  for (let i = 0; i < str.length; i += 1) {

    if (str[i] === 'A') arrDNA.push([str[i], 'T']);
    if (str[i] === 'T') arrDNA.push([str[i], 'A']);
    if (str[i] === 'C') arrDNA.push([str[i], 'G']);
    if (str[i] === 'G') arrDNA.push([str[i], 'C']);
  }
  return arrDNA;
}

pairElement("GCG");

2. Using For Loop, CharAt(), and If Statement

In this solution, we will make use of the traditional for loop and if statements once more in combination with the String object's charAt() method. This method (String.prototype.charAt()) returns the character at the specified index in a string.

function pairElement(str) {
  // Step 1. Create an empty array that will encapsulate other paired arrays
  const arrDNA = [];

  // Step 2. Iterate through the str with a FOR loop 
  for (let i = 0; i < str.length; i += 1) {
    // Step 3. Use if statement to evaluate base pair and push it to arrDNA

    // If the current str character is X create an array of current str with its corresponding pair and push the array to arrDNA

    if (str.chartAt(i) === 'A') // if A
      arrDNA.push([str[i], 'T']); // ...push [A - T]
    else if (chartAt(i) === 'T') // if T 
      arrDNA.push([str[i], 'A']); //...push [T - A]
    else if (chartAt(i) === 'C') // if C
      arrDNA.push([str[i], 'G']); // ...push [C - G]
    else if (chartAt(i) === 'G') // if G
      arrDNA.push([str[i], 'C']); // ...push [G - C]

  }

  // Step 4. Return the 2D array
  return arrDNA;
}

pairElement("GCG");

Without Comments:

function pairElement(str) {
  const arrDNA = [];

  for (let i = 0; i < str.length; i += 1) {

    if (str.chartAt(i) === 'A') 
      arrDNA.push([str[i], 'T']); 
    else if (chartAt(i) === 'T') 
      arrDNA.push([str[i], 'A']); 
    else if (chartAt(i) === 'C') 
      arrDNA.push([str[i], 'G']); 
    else if (chartAt(i) === 'G') 
      arrDNA.push([str[i], 'C']); 

  }

  return arrDNA;
}

pairElement("GCG");

3. Using For...of

The for...of creates a loop iterating over iterable objects (built-in String, Array, Array-like objects).

function pairElement(str) {
  // Step 1. Create an empty array that will encapsulate other paired arrays
  const arrDNA = [];

  // Step 2. Create an object of base pair
  const basePair = {
    'A': 'T',
    'T': 'A',
    'C': 'G',
    'G': 'C'
  }

  // Step 3. Iterate through the str with a for of loop 
  for (const letter of str) {
    // Step 4. Create an array of letter with its corresponding pair and  push to arrDNA
    arrDNA.push([letter, basePair[letter]]);    
  }

  // Step 5. Return the 2D array
  return arrDNA;
}

pairElement("GCG");

Without Comments:

function pairElement(str) {
  const arrDNA = [];
  const basePair = {
    'A': 'T',
    'T': 'A',
    'C': 'G',
    'G': 'C'
  }

  for (const letter of str) {
    arrDNA.push([letter, basePair[letter]]);    
  }
  return arrDNA;
}

pairElement("GCG");

4. Using Split and Map

Let's try to resolve using String.prototype.split() and Array.prototype.map(). The first method (split()) is used to convert a string into an array. The map() method creates a new array with the results of calling a function for every array element.

function pairElement(str) {
  // Step 1. Create an object of base pair
  const basePair = {
    'A': 'T',
    'T': 'A',
    'C': 'G',
    'G': 'C'
  }
   // Step 2. convert the str into an array with split and store the result into arrStr variable
  const arrStr = str.split('');

  /* Step 3. Map through the arrStr and return an array of current value and it baise
  Keep the result of mapping under arrDNA variable
  */
  const arrDNA = arrStr.map(letter => [letter, basePair[letter]])

  // Step 4. Return the 2D array
  return arrDNA;
}

pairElement("GCG");

Without Comments:

function pairElement(str) {
  const basePair = {
    'A': 'T',
    'T': 'A',
    'C': 'G',
    'G': 'C'
  }
  const arrStr = str.split('');

  const arrDNA = arrStr.map(letter => [letter, basePair[letter]])

  return arrDNA;
}

pairElement("GCG");

or even better use split() map() in one line

function pairElement(str) {
  const basePair = {
    'A': 'T',
    'T': 'A',
    'C': 'G',
    'G': 'C'
  }

  return str.split('').map(letter => [letter, basePair[letter]]);
}

pairElement("GCG");

5. Using Split, ForEach, and Switch

In this solution will take help of split(), forEach(), and switch. we have already discussed split() in another solution above. Let's talk a bit about the remaining two:

array.forEach(): this method executes a provided function once for each array element
switch: is similar to if, it gives a more descriptive way to compare a value with multiple variants.

 function pairElement(str) { 
  // Step 1. Create an empty array that will encapsulate other paired arrays
   const arrDNA = []; 

   // Step 2. convert the str into an array with split and store the result into arrStr variable
  const arrStr = str.split('');

  // Step 3. Loop through arrStr using forEach
   arrStr.forEach(x => {
     /* Step 4. Use switch statement to test x and push the corresponding array to arrDNA */
    switch (x) {
      case "G": // in case x = G
       arrDNA.push(["G","C"]); // ...push ["G","C"] to arrDNA
       break // break tells the script to run from the case where the criterion is met      
      case "C":   
       arrDNA.push(["C","G"]);
       break;        
      case "T":
       arrDNA.push(["T","A"]);
       break;       
      case "A":
       arrDNA.push(["A","T"]);
       break;       
    }    
  });

// Step 5. Return the 2D array
  return arrDNA;
}
pairElement("GCG");

Without Comments:

 function pairElement(str) { 
   const arrDNA = []; 

  const arrStr = str.split('');

   arrStr.forEach(x => {

    switch (x) {
      case "G": 
       arrDNA.push(["G","C"]);
       break       
      case "C":   
       arrDNA.push(["C","G"]);
       break;        
      case "T":
       arrDNA.push(["T","A"]);
       break;       
      case "A":
       arrDNA.push(["A","T"]);
       break;       
    }    
  });

  return arrDNA;
}
pairElement("GCG");

Wrap up

That is it for this tutorial. We have used five different ways to solve the DNA Pairing challenge that is available on FreeCodeCamp.

Which of these solutions is fine for you? Do you have any other solutions? Share with us. Among all these solutions if I have to chose just one, I'd go for the 3rd one that makes use of for...of.

If you want read more articles from me, you can go here. Don't hesitate to tell me hello on twitter; I really appreciate it.

I have a live coding session on Friday

Abel Lifaefi Mbula — Wed, 20 May 2020 19:01:50 +0000

Hi there,

I'll be having a live coding session on youtube this.friday May 22, 2020, at 2:25 PM GMT. We'll be building a Calculator in CSS flexbox like this:

Join us if you can and let's have a funny and amazing time.

DEV Community: Abel Lifaefi Mbula

chalk equivalent in Flask

Bubble sort explained to a 6-year-old kid

The bubble sort in a nutshell

Bubble sort in practice

First iteration

Second iteration

Bubble sort: Pseudocode

Bubble sort: Java implementation

Complexity analysis

How to get a user’s LinkedIn account, Twitter username, and more from a single line of code

Kelvin Data 101

How to Setup a Minimal Node.js Server

Goals

Prerequisites

The project initialization

package.json

The file structure

Bootstrapping a Node.js server with Express.js

Serving files

Deal with files and directories

Wrap up

The 15 Algorithm Challenges I Solved in May 2020

-1- Sum All Numbers in a Range

The Challenge Description

My Solution

Alternative Solution and Improvement

Improvement

Alternative Solutions

Resource(s)

-2- Slice and Splice

Resources

-3- Confirm the Ending

-4- Repeat a String

-5- Finders Keepers

-6- Boo who

-7- Where do I Belong

-8- Mutations

-9- Title Case a Sentence

-10- Falsy Bouncer

-11- Diff Two Arrays

-12- Seek and Destroy

-13- Single Number

-14- Counting Bits

-15- K Closest Points to Origin

1 <= K <= points.length <= 10000

-10000 < points[i][0] < 10000

-10000 < points[i][1] < 10000

My FLOSS Project is Launched! Come and Help!

How to Customize the Nano Text Editor in Linux

In-line customization

Permanently set customization rules with .nanorc

Let's discuss DBs

OAuth 2 Spec is misunderstood, why?

Authorization and Authentication For Everyone

Kim Maida ・ Jul 19 '20

How to Add Bootstrap to your Nodejs Project

The Initial Project

Adding Bootstrap CSS

Using a CDN

Using npm

Conclusion

Five Ways to Solve the DNA Pairing Challenge in JavaScript

The Challenge Description

Provided Test Cases

Understanding the Problem

1. Using For Loop, and If Statement

Without comments:

2. Using For Loop, CharAt(), and If Statement

Without Comments:

3. Using For...of

Without Comments:

4. Using Split and Map

Without Comments:

5. Using Split, ForEach, and Switch

Without Comments:

Wrap up

I have a live coding session on Friday

Using `npm`