Alternatively merging two arrays - JavaScript

We are required to write a JavaScript function that takes in two arrays and merges the arrays taking elements alternatively from the arrays.

For example, if the two arrays are:

const arr1 = [4, 3, 2, 5, 6, 8, 9];
const arr2 = [2, 1, 6, 8, 9, 4, 3];

Then the output should be:

const output = [4, 2, 3, 1, 2, 6, 5, 8, 6, 9, 8, 4, 9, 3];

Method 1: Using Index-Based Logic

This approach uses a single loop and alternates between arrays based on even/odd index positions:

const arr1 = [4, 3, 2, 5, 6, 8, 9];
const arr2 = [2, 1, 6, 8, 9, 4, 3];

const mergeAlternatively = (arr1, arr2) => {
    const res = [];
    for(let i = 0; i 

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


Method 2: Using Two Pointers

This approach uses separate pointers for each array, making the logic clearer:

const mergeAlternativelyTwoPointers = (arr1, arr2) => {
    const result = [];
    let i = 0, j = 0;
    
    while(i 

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


Handling Different Array Lengths

Both methods handle arrays of different lengths correctly. Here's an example with unequal arrays:

const shortArr = [1, 2];
const longArr = [10, 20, 30, 40, 50];

console.log("Short + Long:", mergeAlternatively(shortArr, longArr));
console.log("Long + Short:", mergeAlternatively(longArr, shortArr));


Short + Long: [ 1, 10, 2, 20, 30, 40, 50 ]
Long + Short: [ 10, 1, 20, 2, 30, 40, 50 ]


Comparison

Conclusion

Both methods effectively merge arrays alternatively. The two-pointer approach is more readable and intuitive, while the index-based method is more compact for equal-length arrays.