PAT 1051. Pop Sequence (25)

1051. Pop Sequence (25)

时间限制

100 ms

内存限制

65536 kB

代码长度限制

16000 B

判题程序

Standard

作者

CHEN, Yue

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

---

 

模拟堆栈，注意一点：vector删除最后一个数据是vector.erase(vector.end()-1)，而不是vector.erase(vector.end())。

#include <bits/stdc++.h>

using namespace std;

int N, M, K;
int num[1003];
bool flag[1003];

int main()
{
    cin>>M>>N>>K;
    for(int i = 0; i < K; i++) {
        for(int j = 0; j < N; j++) {
            cin>> num[j];
        }
        int index = 0;
        int n = 1;
        vector<int> numVec;
        while(1) {
            if(index == N) break;
            //cout<< index<< ":"<< num[index]<< ":"<< n<< endl;
            if(num[index] > n) {
                numVec.push_back(n);
                if(numVec.size() > M) {
                    flag[i] = true;
                    break;
                }
                n++;
            }
            else if(num[index] == n) {
                //if(flag1 == true)numVec.erase(numVec.end());
                if(numVec.size() == M) {
                    flag[i] = true;
                    break;
                }
                index++;
                n++;
            }
            else if(num[index] < n) {
                if(numVec.size() == 0) {
                    flag[i] = true;
                    break;
                }
                else if(num[index] != numVec[numVec.size()-1]) {
                    flag[i] = true;
                    break;
                }
                numVec.erase(numVec.end()-1);
                index++;
            }
        }
        //cout<< flag[i]<< endl;
    }
    for(int i = 0; i < K; i++) {
        if(flag[i] == true) {
            cout<< "NO"<< endl;
        }
        else {
            cout<< "YES"<< endl;
        }
    }
    return 0;
}