Remove k digits

class Solution:
    def removeKdigits(self, num: str, k: int) -> str:
        numStack = []
        for digit in num:
            while k > 0 and numStack and numStack[-1] > digit:
                numStack.pop()
                k -= 1
            numStack.append(digit)

        res = numStack[:-k] if k > 0 else numStack

        return "".join(res).lstrip('0') or '0'

Remove K Digits

Difficulty: Medium

Given string num representing a non-negative integer num, and an integer k, return the smallest possible integer after removing k digits from num.

 

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.

 

Constraints:

  • 1 <= k <= num.length <= 105
  • num consists of only digits.
  • num does not have any leading zeros except for the zero itself.