PAT甲级1051 Pop Sequence (25分)|C++实现

一、题目描述

原题链接
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

二、解题思路

一道堆栈的模拟题，给定栈的容量，要输入的数字与输入多少组序列，要我们判断每一组序列是不是这个栈可以实现的序列。我们可以将每次输入的序列存放在一个数组order中，我们验证到的数的下标用current表示。接着我们进行一个栈的实现，建立一个循环，每次循环向里面存入一个数，先判断这个栈的大小是否已经超出要求，如果没有，我们就建立一个while循环，若栈顶的值等于order[current]，则弹出，current自增，这样，我们就可以解决这个问题了。

三、AC代码

#include<iostream>
#include<cstdio>
#include<algorithm>
#include<stack>
using namespace std;
int order[1001];
int main()
{
    
    
    int M, N, K, tmp, current;
    bool flag;
    stack<int> st;
    scanf("%d%d%d", &M, &N, &K);
    for(int i=0; i<K; i++)
    {
    
    
        while(!st.empty())  st.pop();
        for(int j=0; j<N; j++)
            scanf("%d", &order[j]);
        current = 0;
        flag = true;
        for(int j=0; j<N; j++)
        {
    
    
            st.push(j+1);
            if(st.size() > M)
            {
    
    
                flag = false;
                break;
            }
            while(!st.empty() && st.top() == order[current])
            {
    
    
                st.pop();
                current++;
            }
        }
        if(st.size()==0 && flag == true)    printf("YES\n");
        else    printf("NO\n");
    }
    return 0;
}