[LeetCode] #32 Longest Valid Parentheses

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.

本题是括号匹配问题，用栈存放‘（’，如果碰到‘）’就出栈。时间：17ms，代码如下：

class Solution {
public:
    int longestValidParentheses(string s) {
        if (s.empty())
            return 0;
        stack< pair<char,int> > validStack;
        for (string::const_iterator iter = s.begin(); iter != s.end(); iter++){
            if (*iter == '(')
                validStack.push(make_pair('(',iter - s.begin()));
            else if (*iter == ')'){
                if (!validStack.empty() && validStack.top().first == '('){
                    validStack.pop();
                }
                else
                    validStack.push(make_pair(*iter,iter - s.begin()));
            }
        }
        if (validStack.empty())
            return s.size();
        int temp = validStack.top().second;
        int max = s.size() - 1 - temp ;
        validStack.pop();
        while (!validStack.empty()){
            if (max < temp - validStack.top().second - 1)
                max = temp - validStack.top().second - 1;
            temp = validStack.top().second;
            validStack.pop();
        }
        if (max < temp)
            return temp;
        return max;
    }
};