[Leetcode]Longest Valid Parentheses

最新推荐文章于 2022-09-01 00:56:47 发布

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本文介绍了一种使用栈来解决寻找字符串中最长合法括号序列的方法，详细解释了算法逻辑，并提供了Python代码实现。

Given a string containing just the characters '(' and ')', find the length of the longest valid (well-formed) parentheses substring.

For "(()", the longest valid parentheses substring is "()", which has length = 2.

Another example is ")()())", where the longest valid parentheses substring is "()()", which has length = 4.

求最长的合法括号序列~用一个栈记录左括号, 右括号和index,并把stack初始为[(-1, ')')]，避免之后处理stack为空的情况~ 如果当前括号是右括号且栈顶是左括号, 则把栈顶弹出并更新maxLen~

class Solution:
    # @param s, a string
    # @return an integer
    def longestValidParentheses(self, s):
        if s is None or len(s) == 0: return 0
        lenS, stack, maxLen = len(s), [(-1, ')')], 0
        for i in xrange(lenS):
            if s[i] == ')' and stack[-1][1] == '(':
                stack.pop()
                maxLen = max(maxLen, i - stack[-1][0])
            else:
                stack.append((i, s[i]))
        return maxLen