PAT甲级——A1051 Pop Sequence

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

 #include <iostream>
 #include <stack>
 using namespace std;
 int M, N, K;
 int main()
 {
     cin >> M >> N >> K;
     for (int i = ; i < K; ++i)
     {
         stack<int>s;
         int a, b = , flag = ;
         for (int j = ; j < N; ++j)
         {
             cin >> a;
             while (s.size() < M && (s.empty() || s.top() != a))
                 s.push(b++);
             if (s.top() == a)
                 s.pop();
             else
                 flag = ;
         }
         if (flag == )
             cout << "Yes" << endl;
         else
             cout << "No" << endl;
     }
     return ;
 }