铁轨（UVa 514)

 1 #include<iostream>
 2 #include<stack>
 3 using namespace std;
 4 #define maxn 1001
 5 int n, num[maxn];
 6 
 7 int main() {
 8     while ((cin >> n)&&n!=0) {
 9         while (n) {
10             for (int i = 1; i <= n; i++) {
11                 cin >> num[i];
12                 if (num[1] == 0) {
13                     n = 0; break;
14                 }
15             }
16             if (n == 0)break;
17             stack<int>s;
18             int A = 1, B = 1;
19             bool flag = true;
20             while (B <= n) {
21                 if (A == num[B]) { A++; B++; }
22                 else if ((!s.empty()) && s.top() == num[B]) { s.pop(); B++; }
23                 else if (A <= n) s.push(A++);
24                 else { flag = false; break; }
25             }
26             cout << (flag ? "Yes" : "No") << endl;
27         }
28         cout << endl;
29     }
30     return 0;
31 }