学步园

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.

思路：

首先扫描一遍，mark所有的成对括号。然后数一下最长的记号。

题解：

class Solution {
public:
    int longestValidParentheses(string s) {
        stack<int> LP;

        for(int i = 0; i < s.size(); ++i)
        {
            char ch  = s[i];
            if (ch == '(')
                LP.push(i);
            else
            {
                if (!LP.empty())
                {
                    s[LP.top()] = ' ';
                    s[i] = ' ';
                    
                    LP.pop();
                }
            }
        }
        
        int longest = 0;
        int curr_len = 0;
        for(auto& ch : s)
            if (ch == ' ')
                curr_len++, longest = max(curr_len, longest);
            else
                curr_len = 0;
        
        return longest;
    }
};