[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.

 

 1 class Solution {
 2 public:
 3     int longestValidParentheses(string s) {
 4         stack<int> stk;
 5         int ret = 0;
 6         
 7         if (s.size() <= 1) return 0;
 8         
 9         stk.push(0);
10         
11         for (int i = 1; i < s.size(); i++){
12             if (!stk.empty() && s[stk.top()] == '(' && s[i] == ')'){
13                 stk.pop();
14             }else{
15                 stk.push(i);  
16             } 
17         }
18         
19         if (stk.empty()){
20             return s.size();
21         }else if (stk.top() != s.size() - 1){
22             stk.push(s.size());
23         }
24         
25         while (!stk.empty()){
26             int tmp = stk.top();
27             stk.pop();
28             if (stk.empty()) {
29                 ret = max(ret, tmp);
30             }else{
31                 ret = max(ret, tmp - stk.top() - 1);
32             }
33         }
34         
35         return ret;
36     }
37 };