// Function to merge two sorted (increasing) arrays of numbers

function mergeTwoSortedArrays(arr1, arr2) {

// Setup pointers (indexes for traversing arrays), and mergedArray array

let ptr1 = 0

let ptr2 = 0

let mergedArray = []

// Check for empty input

if (arr1.length === 0 && arr2.length === 0) return mergedArray // if both arrays empty return empty mergedArray

if (arr1.length === 0) return arr2 // if arr1 is empty return arr2

if (arr2.length === 0) return arr1 // if arr2 is empty return arr1

// While either pointer is not equal to length of their array:

while (ptr1 < arr1.length && ptr2 < arr2.length) {

// Add arr1[ptr1] to mergedArray array and increase ptr1 by 1

if (arr1[ptr1] <= arr2[ptr2]) {

mergedArray.push(arr1[ptr1])

ptr1++

}

// Add arr2[ptr2] to mergedArray array and increase ptr2 by 1

else if (arr1[ptr1] > arr2[ptr2]) {

mergedArray.push(arr2[ptr2])

ptr2++

}

}

// If ptr1 hasn't traversed all of arr1, push these remaining arr1 values to mergedArray

while (ptr1 < arr1.length) {

mergedArray.push(arr1[ptr1])

ptr1++

}

// If ptr2 hasn't traversed all of arr2, push these remaining arr2 values to mergedArray

while (ptr2 < arr2.length) {

mergedArray.push(arr2[ptr2])

ptr2++

}

return mergedArray

}

// Driver code to test above

const array1 = [0, 3, 4, 31]

const array2 = [4, 6, 30]

console.log(mergeTwoSortedArrays(array1, array2)) // [0, 3, 4, 4, 6, 30, 31]