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

A different iterative algorithm:

function flatten2(input) {
  var output = [];
  var todo = [input];
  var current;
  var head;

  while(todo.length) {
    var current = todo.shift();
    if(Array.isArray(current)) {
      current = current.slice();
      head = current.shift();
      if(current.length) {
        todo.unshift(current)
      }

      todo.unshift(head);
    } else {
      output.push(current);
    }
  }

  return output;
}

• Put all elements on a stack.
• While the stack is not empty, remove the first element.
  • If that element is a scalar, add it to the output.
  • If that element is an array, split it into head (first element) and tail (remaining elements) and add both to the stack.

As Tomalak's JSPerf shows, this is pretty slow.

JSBin