Leetcode: 32. Longest Valid Parentheses

Description

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

Example

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

• 用一个栈，将有效的括号匹配表示到一个标志数组中
• 然后变量标志数组，找到最大长度

代码

class Solution {
public:
    int longestValidParentheses(string s) {
        int len = s.size();
        if(len <= 1) return 0;
        
        stack<int> Stack;
        vector<bool> flag(len, false);
        int i = 0, maxLen = 0, tmpLen = 0;
        while(i < len){
            if(s[i] == '('){
                Stack.push(i);
                i++;
            }
            else{
                if(Stack.empty()){
                    i++;
                    continue;
                } 
                
                flag[i] = true;
                flag[Stack.top()] = true;
                Stack.pop();
                i++;
            }
        }
        
        for(i = 0; i < len; ++i){
            if(flag[i])
                tmpLen++;
            else{
                if(tmpLen > maxLen)
                    maxLen = tmpLen;
                    
                tmpLen = 0;
            }
        }
        
        if(tmpLen > maxLen)
            maxLen = tmpLen;
            
        return maxLen;
    }
};