【洛谷 1944】

 1 #include <cstdio>
 2 #include <string>
 3 #include <stack>
 4 #include <iostream>
 5 
 6 std::string s;
 7 
 8 int ans, maxn;
 9 
10 void fs() {
11     std::stack<char> q;
12     int len = s.length();
13     for (int i = 0; i < len; ) {
14         while (s[i] == ‘(‘ || s[i] == ‘[‘ || s[i] == ‘{‘) {
15             q.push(s[i++]);
16         }
17             
18         if (s[i] == ‘)‘) {
19             if (!q.empty() && q.top() == ‘(‘) {　　　　　　　　　　　　　　　　　　　　// ！！！！！判断是否栈空，为此我 RE 了 4 个点
20                 q.pop(), ans += 2, i++;
21                 if (maxn < ans) maxn = ans;
22             } else {
23                 while (s[i] == ‘)‘ || s[i] == ‘]‘ || s[i] == ‘}‘) i++;
24                 while (!q.empty()) q.pop();
25                 ans = 0;
26             }
27         } else if (s[i] == ‘]‘) {
28             if (!q.empty() && q.top() == ‘[‘)  {
29                 q.pop(), ans += 2, i++;
30                 if (maxn < ans) maxn = ans;
31             } else {
32                 while (s[i] == ‘)‘ || s[i] == ‘]‘ || s[i] == ‘}‘) i++;
33                 while (!q.empty()) q.pop();
34                 ans = 0;
35             }
36         } else if (s[i] == ‘}‘) {
37             if (!q.empty() && q.top() == ‘{‘)  {
38                 q.pop(), ans += 2, i++;
39                 if (maxn < ans) maxn = ans;
40             } else {
41                 while (s[i] == ‘)‘ || s[i] == ‘]‘ || s[i] == ‘}‘) i++;
42                 while (!q.empty()) q.pop();
43                 ans = 0;
44             }
45         }
46     }
47     
48 }
49 
50 int main() {
51     freopen("sequence.in", "r", stdin);
52     freopen("sequence.out", "w", stdout);
53     
54     std::cin >> s;
55     
56     fs();
57     
58     printf("%d\n", maxn);
59     return 0;
60 }