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 <stdio.h>
#include <stack>
#include <stdbool.h>

using namespace std;
stack<int> st;

const int maxn = 1010;
int arr[maxn];

int main()
{
    int m, n, t;
    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 cur = 1;
        bool flag = true;
        
        for(int i =1; i <= n; i++)
        {
            st.push(i);      //把i压入栈
            if(st.size() > m)  //控制栈的容量
            {
                flag = false;
                break;
            }

            while(!st.empty() && st.top() == arr[cur])
            {
                st.pop();
                cur++;
            }
        }

        if(st.empty() == true && flag == true)
        {
            printf("YES
");
        }
        else
        {
            printf("NO
");
        }
    }
    
    return 0;
}