Remove K Digits

Description

Given a non-negative integer num represented as a string, remove k digits from the number so that the new number is the smallest possible.

Note:

• The length of num is less than 10002 and will be ≥ k.
• The given num does not contain any leading zero.

Example 1:

Input: num = "1432219", k = 3
Output: "1219"
Explanation: Remove the three digits 4, 3, and 2 to form the new number 1219 which is the smallest.

Example 2:

Input: num = "10200", k = 1
Output: "200"
Explanation: Remove the leading 1 and the number is 200. Note that the output must not contain leading zeroes.

Example 3:

Input: num = "10", k = 2
Output: "0"
Explanation: Remove all the digits from the number and it is left with nothing which is 0.

Solution(javascript)

/**
 * @param {string} num
 * @param {number} k
 * @return {string}
 */
const removeKdigits = function (num, k) {
  const stack = []
  for (const x of num) {
    while (x < stack[stack.length - 1] && k > 0) {
      stack.pop()
      k -= 1
    }
    stack.push(x)
  }
  while (k > 0) {
    stack.pop()
    k--
  }

  return stack.slice(
    stack.findIndex(x => x !== '0'),
  ).join('') || '0'
}