Day19——贪心

打卡题目：leetcode第402题，移掉K位数字
相似题目：738

【代码】

class Solution:
    def removeKdigits(self, num: str, k: int) -> str:
        # 单调栈
        stack = []
        for digit in num:
            while k and stack and digit < stack[-1]:
                stack.pop()
                k -= 1
            stack.append(digit)
        final_stack = stack[:-k] if k else stack
        return "".join(final_stack).lstrip('0') or "0"