铁轨（UVa 514)

　　利用栈实现

C++11 代码如下：

 #include<iostream>
 #include<stack>
 using namespace std;
 #define maxn 1001
 int n, num[maxn];

 int main() {
     while ((cin >> n)&&n!=) {
         while (n) {
             for (int i = ; i <= n; i++) {
                 cin >> num[i];
                 if (num[] == ) {
                     n = ; break;
                 }
             }
             if (n == )break;
             stack<int>s;
             int A = , B = ;
             bool flag = true;
             while (B <= n) {
                 if (A == num[B]) { A++; B++; }
                 else if ((!s.empty()) && s.top() == num[B]) { s.pop(); B++; }
                 else if (A <= n) s.push(A++);
                 else { flag = false; break; }
             }
             cout << (flag ? "Yes" : "No") << endl;
         }
         cout << endl;
     }
     return ;
 }