A solution for https://buttondown.com/cassidoo/archive/if-youre-not-failing-youre-not-trying-reshma/

_README.md

Prerequisite: Deno v2

deno run https://gist.github.com/jihchi/49f89035b39445e99e2a7473e754665a/raw/solve.ts

solve.ts

// three-pointer and merging from the end
function merge(a: number[], b: number[]): number[] {
  let i = a.length - b.length - 1; // point to last "real" element of `a`
  let j = b.length - 1; // point to last element of `b`
  let k = a.length - 1; // point to last element of `a`

  while (j >= 0) {
    if (a[i] > b[j]) {
      a[k] = a[i];
      i--;
    } else {
      a[k] = b[j];
      j--;
    }
    k--;
  }

  return a;
}

console.log(merge([1, 3, 5, 0, 0, 0], [2, 4, 6]));
// output: [1, 2, 3, 4, 5, 6]