PAT 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 <iostream>
#include <stack>
#include <vector>
using namespace std;
int main()
{
  int M,N;
  cin>>M>>N;
  int t;
  cin>>t;
  while(t--)
  {
    stack<int> sta;
    sta.push(0);
    vector<int> v(N,0);
    for(int i = 0; i < N; i++)
    {
      cin>>v[i];
    }
    int idx = 0;
    int num = 1;
    bool flag = true;
    while(idx < N)
    {
      while(sta.top() < v[idx] && sta.size() < M + 1)
      {
        sta.push(num++);
      }
      if(sta.top() == v[idx])
      {
        sta.pop();
        idx++;
      }
      else
      {
        flag = false;
        break;
      }
    }
    if(flag)
      cout<<"YES"<<endl;
    else
      cout<<"NO"<<endl;
  }
  return 0;
}