【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 = 0; i < n; i++) {
            cin >> temp;
            q.push(temp);
        }
        for (int i = 1; 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 0;
}