UVa673 Parentheses Balance (栈)

链接：http://acm.hust.edu.cn/vjudge/problem/19102分析：特别要注意空串情况，还有括号奇数个肯定不合法都可以特判。

 1 #include <iostream>
 2 #include <cstdio>
 3 #include <cstring>
 4 #include <stack>
 5 using namespace std;
 6
 7 int main() {
 8     int n;
 9     cin >> n; getchar();
10     while (n--) {
11         string line;
12         getline(cin, line);
13         if (line.compare("\n") == 0) {
14             printf("Yes"); continue;
15         }
16         if (line.size() % 2) {
17             printf("No\n"); continue;
18         }
19         stack<char> s;
20         bool ok = true;
21         for (int i = 0; i < line.size(); i++) {
22             char ch = line[i];
23             if (ch == ‘(‘) s.push(ch);
24             else if (ch == ‘[‘) s.push(ch);
25             if (ch == ‘)‘)
26                 if (!s.empty() && s.top() == ‘(‘) s.pop();
27                 else { ok = false; break; }
28             else if (ch == ‘]‘)
29                 if (!s.empty() && s.top() == ‘[‘) s.pop();
30                 else { ok = false; break; }
31         }
32         if (ok && s.empty()) printf("Yes\n");
33         else printf("No\n");
34     }
35     return 0;
36 }