Iterative solution for flattening n-th nested arrays in Javascript

Question

Can anyone show me an iterative solution for the following problem? I solved it recursively but struggled with an iterative solution. (Facebook Technical Interv

Answer 1

Here's a solution that flattens in place.

function flatten(arr) {
  var i = 0;

  if (!Array.isArray(arr)) {
    /* return non-array inputs immediately to avoid errors */
    return arr;
  }

  while (i < arr.length) { 
    if (Array.isArray(arr[i])) {
      arr.splice(i, 1, ...arr[i]);
    } else {
      i++;
    }
  }
  return arr;
}

This solution iterates through the array, flattening each element one level of nesting at a time until it cannot be flattened any more.