DEV Community: Edward Mendoza

Linked lists

Edward Mendoza — Sun, 09 Aug 2020 01:27:20 +0000

In today's post, I'm going to talk about the single linked list data structure, so let's begin.

What is a linked list

A Linked List basically is a linear data structure consisting of a collection of elements (nodes) in sequence, nodes don't store in order in the memory, instead each node points to another memory reference.

Implementation

Let's start by implementing the Node class, for our node class we only need two properties for our class, value and next, Value will currently hold the node value and the Next property will contain the next node location.

public class Node {
        public int data;
        public Node next;

        public Node(int data) {
            this.data = data;
        }
    }

public class MyLinkedList {
    Node head;

    public void appendFirst(int data) {
        if (head == null) {
            head = new Node(data);
            return;
        }

        Node newNode = new Node(data);
        newNode.next = this.head;

        this.head = newNode;
    }

    public void appendLast(int data) {
        if (head == null) {
            head = new Node(data);
            return;
        }

        Node currentNode = this.head;
        while (currentNode != null) {
            currentNode = currentNode.next;
        }

        currentNode.next = new Node(data);
    }

    public void removeFirst() {
        if (this.head == null) return;

        this.head = this.head.next;
    }

    public void removeLast() {
        if (this.head == null) return;

        if (this.head.next == null) {
            this.head = null;
            return;
        }

        Node currentNode = this.head;
        while (currentNode.next.next != null) {
            currentNode = currentNode.next;
        }

        currentNode.next = null;
    }

    public void traversal() {
        Node currentNode = this.head;
        while (currentNode != null) {
            currentNode = currentNode.next;
        }
    }
}

In a nutshell, this is the Linked List data structure, when is viable to use them? When we want to add to the beginning of the list since is an O(1) we only need to change next pointer.

Data Structures [Arrays]

Edward Mendoza — Sun, 02 Aug 2020 04:58:34 +0000

Hello there friends, this past week officially started with my job search, which means that I need to start trying to improve what I feel is my weakness so for me was an easy answer data structure 😅. So let's start.

What is an array

An array is a linear data structure consisting of a collection of elements which are stored in contiguous physical memory locations and identified by an index, we have two different ways to work with arrays, onde dimensional and two-dimensional array.

How we can iterate over one-dimensional array

function arrayTraversal(array){
  for(let i = 0; i < array.length; i++){
    console.log(array[i])
  }
}

Arrow functions

Edward Mendoza — Wed, 20 May 2020 04:55:26 +0000

This is my third post, and i will talk about arrow functions, which is a new way to create functions.

Arrow Functions

In this past weeks, we have been working with javascript ES6, and moved into react, and one of the main things that i learn was about arrow functions, im going to describe which are one of the main benefits that i consider it.

Benefits

By using arrow functions, it allow us to manage the this context a bit easier, since is bind by default and the other one i would say is short sintaxis which at the same time makes easier to read/create them.

Examples

function multiply (x,y) {
  return x * y;
}

Let's consider the above example, is the regular way to create a function now let's create the same function but as an arrow function.

let add = (x,y) => {
  return x + y;
}

if no arguments are being pass, we can write the function as follows

let saySomething = () => {}

Even to simplify a bit more, we can even return on the same line of code without {}

let add = ( x, y) => x + y

So this is arrow functions in a brief description

Common errors when learning rails!!!!

Edward Mendoza — Fri, 10 Apr 2020 03:19:53 +0000

Most common errors in rails

Hi everybody, this is my second post and since we already completed the rails module in Flatiron School, i would like to talk about some of the most common errors that i face when i was learning and working with labs.

Number 1

NoMethodError: undefined method '[]' for nil:NilClass
I face this error a lot, when i was working with forms and i was using another model collection to create a drop-down, and basically tell us that we are trying to use a square bracket notation to read a property from an object, but the object is missing, or nil, in my case was because usually i forgot to get the instance variable in the action, lets say in the create action and the validation to save failed, then render the new form again, and is when the error came.

Number 2

ActionController::RoutingError
This error basically is telling us that the user made a request to a specific URL that doesn't exist in our routes file, so when the router try to match with a controller action, i will throw the error.

Number 3

ActionController::ParameterMissing
This error is related to the strong parameters and the way that we construct the params, probably we miss to add the :key for the params hash.

Number 4 & last one

ActionView::Template::Error: undefined local variable or method
This error basically means that we are missing the view for the action that was call, and the easy fix is by only create the file under the folder.

Thats all for this post, hope is useful :)!

First week @Flatiron School

Edward Mendoza — Wed, 18 Mar 2020 16:58:45 +0000