【PAT】1051 Pop Sequence (25)（25 分）

Given a stack which can keep M numbers at most. Push N numbers in the order of 1, 2, 3, ..., N and pop randomly. You are supposed to tell if a given sequence of numbers is a possible pop sequence of the stack. For example, if M is 5 and N is 7, we can obtain 1, 2, 3, 4, 5, 6, 7 from the stack, but not 3, 2, 1, 7, 5, 6, 4.

Input Specification:

Each input file contains one test case. For each case, the first line contains 3 numbers (all no more than 1000): M (the maximum capacity of the stack), N (the length of push sequence), and K (the number of pop sequences to be checked). Then K lines follow, each contains a pop sequence of N numbers. All the numbers in a line are separated by a space.

Output Specification:

For each pop sequence, print in one line "YES" if it is indeed a possible pop sequence of the stack, or "NO" if not.

Sample Input:

5 7 5
1 2 3 4 5 6 7
3 2 1 7 5 6 4
7 6 5 4 3 2 1
5 6 4 3 7 2 1
1 7 6 5 4 3 2

Sample Output:

YES
NO
NO
YES
NO

C++代码如下：

 #include<iostream>
 #include<stack>
 #include<queue>
 using namespace std;

 int main() {
     int m, n, k;
     cin >> m >> n >> k;
     while (k--) {
         int temp;
         stack<int>s;
         queue<int>q;
         for (int i = ; i < n; i++) {
             cin >> temp;
             q.push(temp);
         }
         for (int i = ; i <= n;i++) {
             s.push(i);
             if (s.size() > m) break;
             while (!s.empty() && ( q.front() == s.top() ) ) {
                 q.pop();
                 s.pop();
                 if (q.empty()) break;
             }
         }
         if (q.empty()) cout << "YES" << endl;
         else cout << "NO" << endl;
     }
     return ;
 }