402

class Solution:
    def removeKdigits(self, num: str, k: int) -> str:
        if len(num) == k:
            return '0'
        st = []

        i = 0
        for d in num:
            while k and st and st[-1] > d:
                st.pop()
                k -= 1
            st.append(d)

        end = len(st) - k
        start = 0

        while st and start < len(st) and st[start] == '0':
            start += 1

        return ''.join(st[start:end]) if end > start else '0'