1051 Pop Sequence (25 分)

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

是有点恶心这题， 但是还是挺不错的一道题。

#include <bits/stdc++.h>

using namespace std;
stack<int> st;
int n,m,k;
int an[1005];

int main(){
    cin >> n >> m >> k;
    for(int i = 0; i < k; i ++){
        bool flag = true;
        for(int j = 0; j < m; j ++){
            cin >> an[j];
        }
        while(!st.empty()){
            st.pop();
        }
        int p = 1;
        for(int l = 0; l < m; l++){
            if(p > m){
                flag = false;
                break;
            }
            // cout << p << endl;
            if(an[l] != p){
                st.push(p++);
                // p++;
                if(st.size() > n){
                    flag = false;
                    break;
                }
                l--;
            }else{
                st.push(p++);
                if(st.size() > n){
                    flag = false;
                    break;
                }
                while(!st.empty() && (l < m) && (an[l] == st.top())){
                    // cout << st.top();
                    st.pop();
                    l++;
                }
                // if(st.empty())
                l--;
            }
        }
        if(!st.empty()){
            flag = false;
        }
        if(flag)
            cout << "YES" << endl;
        else
            cout << "NO" << endl;
    }
    return 0;
}