python leetcode 32. Longest Valid Parentheses

涉及到括号判断用栈做即可

class Solution(object):
    def longestValidParentheses(self, s):
        """
        :type s: str
        :rtype: int
        """
        maxlen = 0 
        left = []
        l1 = len(s)
        last = -1
        for i in range(l1):
            if s[i] =='(':
                left.append(i)
            else:
                if not left:
                    last = i
                else:
                    left.pop()
                    if left:
                        maxlen = max(maxlen,i-left[-1])
                    else:
                        maxlen = max(maxlen,i-last)
        return maxlen