LeetCode刷题笔记 32. Longest Valid Parentheses

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

Example 1:

Input: "(()"
Output: 2
Explanation: The longest valid parentheses substring is "()"

Example 2:

Input: ")()())"
Output: 4
Explanation: The longest valid parentheses substring is "()()"

传送门：32. Longest Valid Parentheses

 

评论区解答：

遍历括号时把下标放进堆栈中，保证栈顶的值是当前最后不匹配的右括号的下标，每次出栈时当前括号的下标减去栈顶的值就是当前子串的长度。

class Solution {
public:
    int longestValidParentheses(string s) {
        stack<int> parentheses;
        parentheses.push(-1);
        int res = 0; 
        for(int i=0; i<s.length(); ++i) {
            if(s[i] == '(') 
                parentheses.push(i);
            else {
                parentheses.pop();
                if(parentheses.empty())
                    parentheses.push(i);
                else
                    res = max(res, i - parentheses.top());
            }
        }
        return res;
    }
};