PAT 1051. Pop Sequence (25)

http://pat.zju.edu.cn/contests/pat-a-practise/1051

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 <stdio.h>
#include <stack>
using namespace std;

int main(){
	int m, n, k;
	scanf("%d%d%d", &m, &n, &k);
	while (k--){
		stack<int> s;
		int cur = 1, tmp;
		bool flag = true;
		s.push(1);
		for (int i = 0; i < n; i++){
			scanf("%d", &tmp);
			if (tmp > cur){
				for (int j = cur + 1; j <= tmp; j++)
					s.push(j);
				if (s.size() > m) flag = false;
				cur = tmp;
			}
			else{
				if (s.top() != tmp)
					flag = false;
			}
			s.pop();
		}
		if (flag) printf("YES\n");
		else printf("NO\n");
	}
	return 0;
}