DEV Community: smolthing

leetcode 49. Group Anagrams (python)

smolthing — Mon, 12 Aug 2024 13:34:17 +0000

https://leetcode.com/problems/group-anagrams

Solution 1

class Solution:
    def groupAnagrams(self, strs: List[str]) -> List[List[str]]:
        sortedKeyDict = defaultdict(list)

        for i in strs:
            sortedKey = sorted(i)
            sortedKeyInString = ''.join(sortedKey)
            sortedKeyDict[sortedKeyInString].append(i)

        return list(sortedKeyDict.values())

Use sorted word as dictionary key

Time Complexity: O(nklog(k))
Space Complexity: O(nk)

Solution 2

class Solution:
    def groupAnagrams(self, strs: List[str]) -> List[List[str]]:
        sortedKeyDict = defaultdict(list)

        for i in strs:
            characterFrequency = [0]*26
            for j in i:
                index = ord(j) - ord('a')
                characterFrequency[index] += 1
            sortedKeyDict[tuple(characterFrequency)].append(i)

        return list(sortedKeyDict.values())

Use character frequency count as dictionary key
Convert list to tuple to make it hashable as dictionary key

Time Complexity: O(nk)
Space Complexity: O(nk)

Build a landing page using a react template

smolthing — Mon, 05 Aug 2024 13:31:59 +0000

Goal

In this exercise, you will customize your own landing page using the beautiful Landy template. Landy template is built on top of Create React App.

youtube.com

Visit the Demo Website.

Exercise

1 Change Colors

Replace hardcoded colors with reusable colors.

// colors.ts
export const colors = {
    white: '#FFFFFF',
    blue: '#70D6FF',
    ...
}

export const theme = {
    primary: colors.blue,
    ...
};

// style.ts
import { theme } from '../../styles/colors';
export const Title = styled("h4")`
  font-size: 22px;
  text-transform: capitalize;
  color: ${theme.primary};

  @media screen and (max-width: 414px) {
    padding: 1.5rem 0;
  }
`;

2 Adjust Transitions

Reduce transition distance from react-awesome-reveal library using custom logic.

// Slide transition without the ability to change transition distance
import { Slide, Zoom } from "react-awesome-reveal";
...
return (
    <Slide direction="left">
      <Row> content </Row>
    </Slide>
);

// Create custom transition using Reveal and keyframes
import { Reveal } from "react-awesome-reveal";
import { keyframes } from "@emotion/react";

const fade = keyframes`
  from {
    opacity: 0;
    transform: translate3d(50px, 0, 0);
  }
  to {
    opacity: 1;
    transform: translate3d(0, 0, 0);
  }
`;

...
return ( 
    <Reveal keyframes={fade} duration={1500} triggerOnce={true}>
      <Row> content </Row>
    </Reveal>
);

3 Move Objects

Use increments of 5 in position and size for consistency and predictability.

// before
export const Language = styled("h4")`
  font-size: 22px;
  text-transform: capitalize;
  color: #18216d;

  @media screen and (max-width: 414px) {
    padding: 1.234rem 0;
  }
`;

// after
export const Language = styled("h4")`
  font-size: 20px;
  text-transform: capitalize;
  color: #18216d;

  @media screen and (max-width: 415px) {
    padding: 1rem 0;
  }
`;

4 Change Hover States

Use cursor: pointer to indicate clickable object.

export const MenuOutline = styled(MenuOutlined)<any>`
  cursor: pointer;
  font-size: 20px;
  padding: 15px; // increase click area
`;

5 Customize Shadows

Use solid shadow with the darken method from polished library.

export const StyledButton = styled("button")<any>`
  ...
  box-shadow: `${darken(0.2, theme.button)} 6px 6px 0`;

  &:hover {
    ...
    box-shadow: ${theme.navActive} 6px 6px 0;
  }
`;

6 Change images

Replace images in any format. Download free images from unsplash.

7 Add scroll transition to images

Add scroll transition using CSS from wesbos's tutorial.

8 Deploy Website

Deploy react app using github pages from this awesome tutorial.

Getting Started

Go to https://github.com/smolthing/landing-page-landy

`before-landing` folder

This folder contains the initial template and all the necessary files that you will work on.

`after-landing` folder

This folder contains the completed solution, which you can refer to if needed.

Running the app

1 Go into before-landing folder and run the app. The app runs on http://localhost:3000. Run the commands in the terminal:

cd before-landing
npm start

2 Make the necessary changes as per the exercise tasks.
3 Compare your work with the files in the after folder if you need any guidance or reference.
4 Deploy your website by running the command npm run deploy.

Set.of().contains(null)

smolthing — Mon, 15 Jan 2024 16:55:52 +0000

raises a NullPointerException.

import java.util.*;

public class NullPointer {
    public static void main(String[] args) {
        Set<Integer> hashSetContainsNull = new HashSet<>();
        hashSetContainsNull.add(null);
        hashSetContainsNull.contains(null);

        // hashSetAllowsNull [null, 1]
        System.out.println("hashSetContainsNull " + hashSetContainsNull);

        Set<Integer> setOfNotContainsNull = Set.of();
        // Even `contains` will throw NullPointerException
        setOf.contains(null);

        // Exception in thread "main" java.lang.NullPointerException
        // at java.base/java.util.Objects.requireNonNull(Objects.java:208)
        // at java.base/java.util.ImmutableCollections$SetN.contains(ImmutableCollections.java:937)
        System.out.println("setOf " + setOfNotContainsNull);
    }
}

I encountered an unexpected NullPointerException while reusing an empty set validation check in multiple handlers. The issue stemmed from using .contains with different types of empty sets.

One handler gave back Set.of(), which doesn't accept null elements; trying .contains with null would cause an issue. Meanwhile, the other handler returned a HashSet, where null elements can be stored.

I solve the NullPointerException by using Collections.emptySet() instead of Set.of(). Tada.

Some notes on Bash Shell Script

smolthing — Wed, 26 Jul 2023 17:25:16 +0000

#! Shebang

#! /bin/bash

Tell OS to use bash shell (interpreter) to run the script.

Declaring Variable

list_of_variables=("put" "like" "this")
list_of_variables+=("you" "can" "append" "more")
list_of_variables+=("even" "more" "list_of_variables+=")

If statement with environment variable

if [ "$ENABLE_DD_PROFILE" = "true" ]; then
  echo "something"
fi

Print variable

The java_args[@] syntax is used to access the elements of the java_args array. The @ symbol tells Bash to expand the array, so that the individual elements of the array are passed to the Java program as arguments.

# method 1 to print all the arguments
for arg in ${java_args[@]}; do
  echo $arg
done

# method 2 to print all the arguments
printf "%s\n" "${java_args[@]}"

Example of a non working java command bash shell script

#! /bin/bash

java_args=(
    "-Xmx1024m" # max heap size
    "-Xms512m" # min heap size
    "-XX:+HeapDumpOnOutOfMemoryError"
    "-XX:HeapDumpPath=./temp/heapdump"
    )

if [ "$ENABLE_DD_PROFILE" = "true" ]; then
java_args+=(
    "-javaagent:dd-java-agent.jar"
    "-Ddd.service=<YOUR_SERVICE>"
    "-Ddd.env=<YOUR_ENVIRONMENT>"
    "-Ddd.version=<YOUR_VERSION>"
    "-Ddd.profiling.enabled=true"
    "-XX:FlightRecorderOptions=stackdepth=256"
    )
fi

# if -cp and paths are placed before the javaagent, my java would not run correctly somehow. 
java_args+=(
    "-cp"
    "lib/*"
    "lib2/*"
    "-jar <YOUR_SERVICE>.jar"
    )

# print all the arguments
printf "%s\n" "${java_args[@]}"

# run java command
java ${java_args[@]}

Run command

You need to chmod a shell script so that it can be executed by the user. By default, a newly created file has no execute permissions, which means that it cannot be run. The chmod command is used to change the permissions of a file.

chmod +x make the script executable.

$ export ENABLE_DD_PROFILE=true
$ chmod +x java_args.sh && ./java_args.sh
-Xmx1024m
-Xms512m
-XX:+HeapDumpOnOutOfMemoryError
-XX:HeapDumpPath=./temp/heapdump
-javaagent:dd-java-agent.jar
-Ddd.service=<YOUR_SERVICE>
-Ddd.env=<YOUR_ENVIRONMENT>
-Ddd.version=<YOUR_VERSION>
-Ddd.profiling.enabled=true
-XX:FlightRecorderOptions=stackdepth=256
-cp
lib/*
lib2/*
-jar <YOUR_SERVICE>.jar
Error opening zip file or JAR manifest missing : dd-java-agent.jar
Error occurred during initialization of VM
agent library failed to init: instrument

The Java error is intentional, as the main goal is to showcase my new knowledge of bash shell scripts.

Kthxbye.

11. Container With Most Water

smolthing — Fri, 14 Jul 2023 17:46:57 +0000

Question

Find two lines that together with the x-axis form a container, such that the container contains the most water. Return the maximum amount of water a container can store.

Steps

Two pointers: start and end
Choose the shorter height for area
Move the pointer with shorter height

Python

class Solution:
    def maxArea(self, height: List[int]) -> int:

        start = 0
        end = len(height) - 1

        maxArea = 0

        while start < end:
            minHeight = min(height[start], height[end])
            length = end - start
            maxArea = max(maxArea, length * minHeight)

            if height[start] > height[end]:
                end -= 1
            else:
                start += 1

        return maxArea

height =
[3,5,2,6,5,2]

Output = 15

Java

class Solution {
    public int maxArea(int[] height) {
        int maxArea = 0;
        int left = 0;
        int right = height.length - 1;

        while (left < right) {
            int minHeight = Math.min(height[left], height[right]);
            int length = right - left;
            maxArea = Math.max(maxArea, length * minHeight);

            if (height[left] < height[right]) {
                left += 1;
            } else {
                right -= 1;
            }
        }

        return maxArea;
    }
}

Almost all the types in Java

smolthing — Sun, 09 Jul 2023 18:18:25 +0000

Java Data Types - group of objects

Basic Examples

// example.java

import java.lang.Boolean;
import java.lang.Double;
import java.lang.Float;
import java.lang.Integer;
import java.lang.Long;
import java.lang.String;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.HashSet;
import java.util.LinkedList;
import java.util.Map;
import java.util.Set;

public class Example {
    public static void main(String[] args) {
        // Primitive types
        byte myByte = 127; // 8-bit, 2^8, -128 to 127
        short myShort = 32767; // 16-bit, 2^16. -32768 to 32767
        int myInt = 2147483647; // 32-bit, 2^32, -2147483648 to -2147483647
        long myLong = 9223372036854775807L; // 64-bit, 2^64, -9223372036854775808 to 9223372036854775807L, L otherwise
        float myFloat = 3.14f; // 32-bit, 2^32, 
        double myDouble = 3.141592653589793; // 64-bit, 2^64
        char myChar = 'A'; // 16-bit, 2^16, 
        boolean myBoolean = true; // 1-bit, 2^1

        // Reference types
        String myString = "Hello, world!";
        Class myClass = String.class;
        Object myObject = new Object();

        // Collection data types
        ArrayList<String> myArrayList = new ArrayList<>();
        myArrayList.add("Apple");
        myArrayList.add("Orange");
        myArrayList.add("Banana");

        LinkedList<String> myLinkedList = new LinkedList<>();
        myLinkedList.add("Apple");
        myLinkedList.add("Orange");
        myLinkedList.add("Banana");

        Set<String> mySet = new HashSet<>();
        mySet.add("Apple");
        mySet.add("Orange");
        mySet.add("Banana");

        Map<String, Integer> myMap = new HashMap<>();
        myMap.put("Apple", 1);
        myMap.put("Orange", 2);
        myMap.put("Banana", 3);

        // Print out the result
        System.out.println("myByte: " + myByte);
        System.out.println("myShort: " + myShort);
        System.out.println("myInt: " + myInt);
        System.out.println("myLong: " + myLong);
        System.out.println("myFloat: " + myFloat);
        System.out.println("myDouble: " + myDouble);
        System.out.println("myChar: " + myChar);
        System.out.println("myBoolean: " + myBoolean);

        System.out.println("myString: " + myString);
        System.out.println("myClass: " + myClass);
        System.out.println("myObject: " + myObject);

        System.out.println("myArrayList: " + myArrayList);
        System.out.println("myLinkedList: " + myLinkedList);
        System.out.println("mySet: " + mySet);
        System.out.println("myMap: " + myMap);
    }
}

Results

$ java ./example.java
myByte: 127
myShort: 32767
myInt: 2147483647
myLong: 9223372036854775807
myFloat: 3.14
myDouble: 3.141592653589793
myChar: A
myBoolean: true
myString: Hello, world!
myClass: class java.lang.String
myObject: java.lang.Object@3745e5c6
myArrayList: [Apple, Orange, Banana]
myLinkedList: [Apple, Orange, Banana]
mySet: [Apple, Orange, Banana]
myMap: {Apple=1, Orange=2, Banana=3}

1. Set <-- HashSet

In 3Sum, we use hashset to improve lookup time for duplicate values.

...
Set<List<Integer>> set = new HashSet<>();
set.add(Arrays.asList(1, 2, 3)); 
return new ArrayList<>(set);
...

HashSet is a class that implements the Set interface in Java

Methods

Set<List<Integer>> set = new HashSet<>(); // slow, less memory used
HashSet<List<Integer>> set = new HashSet<>(); // fast, more memory

Set = abstract class with basic functionality
HashSet = concrete class that implements Set interface

set.iteractor()/toArray()/add()/remove()/contains()/size()/isEmpty()
hashset.add()/remove()/contains()/size()/isEmpty()

Convert ArrayList to/from HashSet

HashSet<String> hashSet = new HashSet<>();
hashSet.add("why so many types");
ArrayList<String> arrayList = new ArrayList<>(hashSet);

HashSet<String> hashSet = new HashSet<>();
hashSet.add("help my brain");
ArrayList<String> arrayList = (ArrayList<String>) hashSet.toArray();

Others

I will update them in the future. My brain is on max CPU at the moment.

3Sum

smolthing — Thu, 06 Jul 2023 18:27:25 +0000

The question

Given an integer array nums, return all the triplets [nums[i], nums[j], nums[k]] such that i != j, i != k, and j != k, and nums[i] + nums[j] + nums[k] == 0.

The idea

Array must be sorted.
Iterate through the list + Left and right pointer.
Result must be a set because they may be duplicate values.
Order of the tuple (current value, left pointer, right pointer) inserted into result matters.

Python

class Solution:
    def threeSum(self, nums: List[int]) -> List[List[int]]:
        result = set()
        nums.sort()
        for i in range(len(nums) - 2):
            currentValue = nums[i]

            left = i + 1
            right = len(nums) - 1

            while left < right:
                totalSum = currentValue + nums[left] + nums[right]
                if totalSum > 0:
                    right -= 1 // if there is no negative value, left += 1 will only increase totalSum
                elif totalSum < 0:
                    left += 1
                else:
                    result.add((currentValue, nums[left], nums[right]))
                    left += 1
                    right -= 1

        return result

Java

class Solution {
    public List<List<Integer>> threeSum(int[] nums) {
        Arrays.sort(nums);
        Set<List<Integer>> set = new HashSet<>();

        for (int i = 0; i<nums.length - 2; i++) {
            int currentValue = nums[i];

            int start = i + 1;
            int end = nums.length - 1;

            while (start < end) {
                int total = currentValue + nums[start] + nums[end];
                if (total < 0) {
                    start += 1;
                } else if (total > 0) {
                    end -= 1;
                } else {
                  set.add(Arrays.asList(currentValue, nums[start], nums[end]));
                    start += 1;
                    end -= 1;
                }
            }
        }

        return new ArrayList<>(set);
    }
}

How to create a tag release

smolthing — Sun, 02 Jul 2023 19:23:52 +0000

How to create a tag release for this tutorial.

Run commands:

git fetch --tag
git tag
git tag -a v1.0.0 -m "The beginning of smolthing backend"
git push origin --tag

Tada 🎉 https://github.com/smolthing/backend/releases/tag/v1.0.0

Build web application in Vert.x [Part 1/ ♾️]

smolthing — Sun, 02 Jul 2023 19:11:19 +0000

TL;DR: Start a simple vert.x web application with health check.

Steps

Download Vertx Starter.zip: Java, Gradle and everything nice. Or you can use my exquisite buffet selection below:

curl -G https://start.vertx.io/starter.zip -d "groupId=com.example" -d "artifactId=starter" -d "vertxVersion=4.4.4" -d "vertxDependencies=vertx-web,vertx-web-client,vertx-web-graphql,vertx-web-sstore-redis,vertx-web-sstore-cookie,vertx-web-validation,vertx-web-openapi,vertx-service-discovery,vertx-circuit-breaker,vertx-config,vertx-kafka-client,vertx-consul-client,vertx-tcp-eventbus-bridge,vertx-micrometer-metrics,vertx-health-check,vertx-junit5,vertx-zookeeper,vertx-grpc-server,vertx-grpc-client,vertx-service-proxy,vertx-grpc-context-storage,vertx-http-service-factory,vertx-json-schema,vertx-shell" -d "language=java" -d "jdkVersion=11" -d "buildTool=gradle" --output starter.zip

Run command: ./gradlew run
Go to http://localhost:8888
Add a router and health check using Using Vert.x Health Checks a. Add

import io.vertx.core.AbstractVerticle;
import io.vertx.core.Promise;
import io.vertx.ext.healthchecks.HealthCheckHandler;
import io.vertx.ext.healthchecks.HealthChecks;
import io.vertx.ext.web.Router;

public class MainVerticle extends AbstractVerticle {

  @Override
  public void start(Promise<Void> startPromise) throws Exception {
    HealthCheckHandler healthCheckHandler = HealthCheckHandler
      .createWithHealthChecks(HealthChecks.create(vertx));
    HealthCheckManager.configureHealthChecks(healthCheckHandler);

    Router router = Router.router(vertx);
    router.get("/ping").handler(healthCheckHandler);
    router.get("/*").handler(routingContext -> {
      routingContext.response()
        .putHeader("content-type", "text/plain; charset=utf-8")
        .end("Hello smolthing \uD83D\uDCA9.");
    });

    vertx.createHttpServer().requestHandler(router).listen(8888, http -> {
      if (http.succeeded()) {
        startPromise.complete();
        System.out.println("HTTP server is running on port 8888");
      } else {
        startPromise.fail(http.cause());
      }
    });
  }
}

import io.vertx.ext.healthchecks.HealthCheckHandler;
import io.vertx.ext.healthchecks.Status;

public class HealthCheckManager {
  public static void configureHealthChecks(HealthCheckHandler healthCheckHandler) {
    healthCheckHandler.register("App connection", promise -> {
      promise.complete(Status.OK());
    });
  }
}

DEV Community: smolthing

leetcode 49. Group Anagrams (python)

Solution 1

Solution 2

Build a landing page using a react template

Goal

Exercise

Getting Started

before-landing folder

after-landing folder

Running the app

Set.of().contains(null)

Some notes on Bash Shell Script

#! Shebang

Declaring Variable

If statement with environment variable

Print variable

Example of a non working java command bash shell script

Run command

11. Container With Most Water

Question

Steps

Python

Java

Almost all the types in Java

Java Data Types - group of objects

Basic Examples

Results

1. Set <-- HashSet

Methods

Convert ArrayList to/from HashSet

Others

3Sum

The question

The idea

Python

Java

How to create a tag release

Build web application in Vert.x [Part 1/ ♾️]

TL;DR: Start a simple vert.x web application with health check.

Steps

Reference

`before-landing` folder

`after-landing` folder