【PTA-A】1051 Pop Sequence (25 分)（栈）

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;
const int MAX=1010;
int a[MAX];
stack<int> st;
int main() {
	int m, n, t; cin >> m >> n >> t;
	while (t--) {
		while (!st.empty())st.pop();
		for (int i = 1; i <= n; i++)cin >> a[i];
		int cur = 1,flag=1;
		for (int i = 1; i <= n; i++) {
			st.push(i);
			if (st.size() > m) {
				flag = 0;
				break;
			}
			while (!st.empty() && st.top() == a[cur]) {
				st.pop();
				cur++;
			}
		}
		if (st.empty() == true && flag == 1)
			cout << "YES" << endl;
		else cout << "NO" << endl;
	}
	return 0;
}