[Leetcode] Longest Valid Parentheses

最新推荐文章于 2022-09-01 00:56:47 发布

liuwenyirachel

最新推荐文章于 2022-09-01 00:56:47 发布

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分类专栏： Leetcode

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本文探讨如何在给定的字符串中找到最长的有效括号子串，通过使用栈数据结构来解决这个问题。

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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.

#include <stack>
using namespace std;

class Solution {
public:
    int longestValidParentheses(string s) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
       
       int maxLength = 0;
       int size = s.size();
       stack<int> left; 
       if(size<=0) return 0;
       int top = size;
       
       for(int i = 0; i<size; i++)
       {
           if(s[i]=='(')
           {
               left.push(i);
           }
           else
           {
               if(left.empty())
               {
                   top = i + 1;//指向下一个为")"的index
               }
               else
               {
                   int tmp = left.top();
                   top = min(top,tmp);
                   left.pop();
                   if(left.empty()) maxLength = max(i-top+1,maxLength);
                   else maxLength = max(i-left.top(),maxLength); //注意：为什么是left.top()而不是tmp-1呢？考虑"(()()"的情况。
               }
           }
       }
       
       return maxLength;
    }
};