LeetCode Online Judge 题目C# 练习 - Longest Valid Parentheses

最新推荐文章于 2025-08-24 09:29:29 发布

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最新推荐文章于 2025-08-24 09:29:29 发布

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文章标签：数据结构与算法

原文链接：http://www.cnblogs.com/etcow/archive/2012/09/21/2696264.html

本文介绍了一种O(n)复杂度的算法，用于在给定字符串中找到最长的有效括号子串，并详细解释了算法实现过程及示例。

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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.

 1         public static int LogestValidParentheses(string s)
 2         {
 3             if (s.Length <= 1)
 4                 return 0;
 5 
 6             Stack<int> stack = new Stack<int>();
 7 
 8             int start = s.Length;
 9             int curr_length = 0;
10             int max_length = 0;
11 
12             for(int i = 0; i < s.Length; i++)
13             {
14                 if (s[i] == '(')
15                     stack.Push(i);
16 
17                 if (s[i] == ')')
18                 {
19                     //if invalid parentheses in the middle set start back to s.Length
20                     if (stack.Count == 0)
21                     {
22                         start = s.Length;
23                     }
24                     else
25                     {
26                         start = Math.Min(start, stack.Pop());
27                         if (stack.Count == 0)
28                         {
29                             curr_length = i - start + 1;
30                             max_length = Math.Max(curr_length, max_length);
31                         }
32                         else
33                         {
34                             //if some left parentheses indices in the stack
35                             curr_length = i - stack.Peek();
36                             max_length = Math.Max(curr_length, max_length);
37                         }
38                     }
39                 }
40             }
41 
42             return max_length;
43         }