1
var removeKdigits = function (num, k) {
2
  if (k == num.length) {
3
    return "0";
4
  }
5
  let stack = [];
6
  for (let i = 0; i < num.length; i++) {
7
    while (stack.length > 0 && num[i] < stack[stack.length - 1] && k > 0) {
8
      stack.pop();
9
      k--;
10
    }
11
    stack.push(num[i]);
12
  }
13
  while (k > 0) {
14
    stack.pop();
15
    k--;
16
  }
17
  while (stack[0] == 0 && stack.length > 1) {
18
    stack.shift();
19
  }
20
  return stack.join("");
21
};