1051. Pop Sequence (25)

题目连接：https://www.patest.cn/contests/pat-a-practise/1051原题如下：

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

我觉得这道题对我来说已经很难了，难在逻辑关系上。我刚开始没想到用一个数去记录push进堆栈的元素的数字，并在刚开始判断数是否大于
当前可以push进的元素的最大值。每当pop的时候，可以Push进的元素的最大值++。
参考了别人的代码：

#include<stdio.h>
#include<stack>
#define MAXN 1005
using namespace std;

int main()
{
    int M,N,K;
    scanf("%d %d %d",&M,&N,&K);
    int sequence[MAXN];
    while (K--)
    {
        for (int i=0;i<N;i++)scanf("%d",&sequence[i]);
        int MaxNum,flag,index;
        MaxNum=M;
        flag=1;
        index=1;
        stack<int>s;

        for (int i=0;i<N;i++)
        {
            if (sequence[i]>MaxNum)
            {
                flag=0;//printf("%d afds
",sequence[i]);
                break;
            }
            else
            {
                while (s.empty() || (!s.empty()&&s.top()!=sequence[i]&&index<=sequence[i]))
                {
                   // printf("%d %d
",index,sequence[i]);
                    s.push(index++);
                }
                if (s.top()!=sequence[i])
                {
                    flag=0;//printf("%d
",sequence[i]);
                    break;
                }
            }
            s.pop();
            MaxNum++;
        }

        if (flag)printf("YES
");
        else printf("NO
");
    }
    return 0;
}