PAT 1051 Pop Sequence 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<cstdio>
#include<stack>
using namespace std;
stack<int>st;
int main(){
	int m,n,T;
	int arr[1010];
	scanf("%d%d%d",&m,&n,&T);
	while(T--){
		while(!st.empty()){ 
			st.pop();
		} 
		for(int i=1;i<=n;i++)
			scanf("%d",&arr[i]);
		int index=1;
		bool flag=true;
		for(int i=1;i<=n;i++){
			st.push(i);
			if(st.size()>m){
				flag=false;
				break;
			}
			//啊啊啊啊这里写while啊 写成了if...
			while(!st.empty()&&st.top()==arr[index]){
				index++;
				st.pop();
			}
		}
		if(st.empty()==true &&flag)
			printf("YES\n");
		else
			printf("NO\n");
	}
}