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JavaScript Program to Merge two Sorted Arrays into a Single Sorted Array

In this article, we will cover how to merge two sorted arrays into a single sorted array in JavaScript.

Given there are two sorted arrays, we need to merge them into a single sorted array in JavaScript. We will see the code for each approach along with the output. Below are the possible approaches that will be discussed in this article:

Approaches to merge two sorted arrays into a single sorted array

Table of Content

Using the concat() and slice() methods in JavaScript

Here, we are going to basically use the basic concat() and slice() functions of JavaScript that will concat the arrays which we will give as input, and slice() will extract the positions of the arrays given as input.

Example: In this example, we are using concat() and slice() methods in JavaScript

JavaScript 
// Using concat() and slice() method
function mergeSortedArrayUsingConcat(array1, array2) {
    let sortedArray = [],
        Array1Index = 0,
        Array2Index = 0;
    while (
        Array1Index < array1.length &&
        Array2Index < array2.length
    ) {
        if (
            sortFunc(
                array1[Array1Index],
                array2[Array2Index]
            ) > 0
        ) {
            sortedArray.push(array2[Array2Index++]);
        } else {
            sortedArray.push(array1[Array1Index++]);
        }
    }
    if (Array2Index < array2.length) {
        sortedArray = sortedArray.concat(
            array2.slice(Array2Index)
        );
    } else {
        sortedArray = sortedArray.concat(
            array1.slice(Array1Index)
        );
    }
    return sortedArray;
}
function sortFunc(a, b) {
    return a - b;
}
console.log(
    mergeSortedArrayUsingConcat(
        [1, 2, 3, 5, 9],
        [4, 6, 7, 8]
    )
);

Output
[
  1, 2, 3, 4, 5,
  6, 7, 8, 9
]

Using the Array.reduce() method in JavaScript

Here, we will use the reduce() function which is in the Array library. This function is similar to the spread operator as seen in the above approach. reduce(0 function mainly operates on the array and reduces the array to a single value.

Example: In this example, we are going to use Array.reduce() method in JavaScript.

JavaScript 
//Using Array.reduce() and shift method method
function mergeSortedArraysUsingReduce(array1, array2) {

    // Using array.reduce to generate new sorted array
    let singleMergedArray = array1.reduce(
        (outputVar, array1Element) => {
            while (
                array2.length &&
                array2[0] < array1Element
            ) {
                outputVar.push(array2.shift());
            }
            outputVar.push(array1Element);
            return outputVar;
        },
        []
    );

    return singleMergedArray.concat(array2);
}
let array1 = [1, 2, 3, 5, 9];
let array2 = [4, 6, 7, 8];
const outputArray = mergeSortedArraysUsingReduce(
    array1,
    array2
);
console.log(outputArray);

Output
[
  1, 2, 3, 4, 5,
  6, 7, 8, 9
]

Using Two Pointers

Using two pointers, initialize two indices for the two arrays. Compare elements at these indices, add the smaller element to the result array, and move the corresponding pointer forward. Repeat until one array is fully processed, then add remaining elements from the other array.

Example: In this example the function mergeSortedArraysTwoPointers merges two sorted arrays into one sorted array using two pointers.

JavaScript 
function mergeSortedArraysTwoPointers(arr1, arr2) {
  let result = [];
  let i = 0, j = 0;

  while (i < arr1.length && j < arr2.length) {
    if (arr1[i] <= arr2[j]) {
      result.push(arr1[i]);
      i++;
    } else {
      result.push(arr2[j]);
      j++;
    }
  }

  // Add remaining elements from arr1
  while (i < arr1.length) {
    result.push(arr1[i]);
    i++;
  }

  // Add remaining elements from arr2
  while (j < arr2.length) {
    result.push(arr2[j]);
    j++;
  }

  return result;
}

let arr1 = [1, 3, 5];
let arr2 = [2, 4, 6];
console.log(mergeSortedArraysTwoPointers(arr1, arr2));

Output
[ 1, 2, 3, 4, 5, 6 ]




Reffered: https://www.geeksforgeeks.org

JavaScript

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Type:
 Geek
Category:
 Coding
Sub Category:
 Tutorial
Uploaded by:
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