有效括号问题

题目

20. Valid Parentheses

解法

遇到左括号时push，遇到右括号pop。

    def isValid(self, s):
        """
        :type s: str
        :rtype: bool
        """
        stack = []
        dict = {"]":"[", "}":"{", ")":"("}
        for char in s:
            if char in dict.values():
                stack.append(char)
            elif char in dict.keys():
                if stack == [] or dict[char] != stack.pop():
                    return False
            else:
                return False
        return stack == []

等待时间问题

题目

739. Daily Temperatures

解法

将天数指针存入堆栈中，当遇到更暖和的天气时，从堆栈中pop()。

    def dailyTemperatures(self, T):
        """
        :type T: List[int]
        :rtype: List[int]
        """
        ans = [0] * len(T)
        stack = []
        for i, t in enumerate(T):
          while stack and T[stack[-1]] < t:
            cur = stack.pop()
            ans[cur] = i - cur
          stack.append(i)
        return ans