88.js

/** ------------------------------------------------------------------------------
 * 
 * 88. Merge Sorted Array
 * Topics: Array, Two Pointers
 * https://leetcode.com/problems/merge-sorted-array/description/
 * 
 ------------------------------------------------------------------------------ */
var merge = function (nums1, m, nums2, n) {
  let p1 = m - 1
  let p2 = n - 1

  for (let i = m + n - 1; i >= 0; i--) {
    if (p2 < 0) break

    if (p1 >= 0 && nums1[p1] > nums2[p2]) {
      nums1[i] = nums1[p1]
      p1--
    } else {
      nums1[i] = nums2[p2]
      p2--
    }
  }
  return nums1
}

console.log(merge([1, 2, 3, 0, 0, 0], 3, [2, 5, 6], 3))