Concatenation Of Array

Different approaches to solve this problem in JavaScript

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Problem Statement:

Given an integer array num of length n, you want to create an array ans of length 2n where ans[i] == nums[i] and ans[i + n] == nums[i] for 0 <= i < n (0-indexed). Specifically, ans is the concatenation of two nums arrays.

In JavaScript, the concatenation of two arrays is the process of merging the elements of two arrays into a single array. This can be done using the concat() method, which returns a new array consisting of the elements of the original array followed by the elements of the argument array(s).

Approach 1: Arrays are dynamic in JavaScript

1. Declare an empty array result.
2. Iterate through the array arrand for each element assign the same to the result[i] and result[i + arr.length] .

// ES6 Arrow Function
const concatenationArray = arr => {
    let result = [];

    for(let i  = 0; i < arr.length; i++) {
        result[i] = arr[i];
        result[i + arr.length] = arr[i];
    }

    return result;
}

Time Complexity: O(N)

Space Complexity: O(N)

Approach 2: Constant space

1. Store the length of the array arr in a variable n and then run a loop n times and push the elements in the same array.

// ES6 Arrow Function
const concatenationArray = arr => {
    let n = arr.length;
    for(let i = 0; i < n; i++) {
        arr.push(arr[i]);
    }

    return arr;
}

Time Complexity: O(n)

Space Complexity: O(1)

Note: Here are some fun ways to concatenate the array using the built in functions and operators in JavaScript like concat and spread.

Note: Time and Space for these are going to be linear.

// ES6 Arrow Function
const concatenationArray = arr => [...arr, ...arr];

// ES6 Arrow Function
const concatenationArray = arr => arr.concat(arr);

I hope this article has provided you with valuable insights and helped you better understand the different approaches to solve this problem. Happy Coding!

Problem - Leetcode 1929