PAT-A-1051-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

Code

//思路：用栈来实际模拟出栈序列，关键是要注意栈的大小限制和控制出栈的while循环
#include <iostream>
#include <stack>
using namespace std;

int main(){
	
	int M,N,K;
	scanf("%d%d%d",&M,&N,&K);
    stack<int> stk;
    int *nums =new int[N];
    for(int i=0;i<K;i++){
        while(!stk.empty())
            stk.pop();

        //读入N个数   
        for(int j=0;j<N;j++)
            scanf("%d",&nums[j]);
    
        //比较指针
        int point=0;bool flag =true;
        for(int i=1;i<=N;i++){
            stk.push(i);
            if((int)stk.size()>M){
                flag=false;
                break;
            }
            while(!stk.empty()&&nums[point]==stk.top()){
                stk.pop();
                point++;
            }
        }
        if(stk.empty()&&flag)
            printf("YES\n");
        else    
            printf("NO\n");
    }

	return 0;
}