PAT甲级1051. Pop Sequence (25)

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>using namespace std;#include <stack>#include <vector>int main(){    int M,N,K;    scanf("%d %d %d",&M,&N,&K);    vector<int> V(N);    for(int k=0;k<K;k++){        stack<int> S;        S.push(0);        int flag=1;        int current=0;        for(int i=0;i<N;i++){            scanf("%d",&V[i]);            if(flag){                if(S.top()<V[i]){                    for(int m=current+1;m<=V[i];m++) {                        S.push(m);                        if(S.size()>M+1) {                            flag=0;                            break;                        }                    }                    S.pop();                    current=V[i];                }                else if(S.top()==V[i]) S.pop();                else flag=0;            }        }        if(flag) printf("YES\n");        else printf("NO\n");    }    return 0;}