2020-05-05

1051 Pop Sequence (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

#include<iostream>
#include<vector>
#include<stack>
using namespace std;
int main(){
    int m,n,k;
    scanf("%d %d %d",&m,&n,&k);
    for(int i=0;i<k;++i){
        bool flag = false;
        vector<int> a(n+1);
        stack<int> b;
        int temp;
        for(int j=1;j<=n;++j){
            scanf("%d",&a[j]);
        }
        int index = 1;
        for(int q=1;q<=n;++q){
            b.push(q);
            if(b.size() > m){
                break;
            }
            while(!b.empty() && b.top()==a[index]){
                b.pop();
                index++;
            }
        }
        if(index == n+1){
            flag = true;
        }
        if(flag){
            printf("YES\n");
        }else{
            printf("NO\n");
        }
    }
}