Submission #10315962

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Source Code Expand

#include <bits/stdc++.h>
#define int long long
using namespace std;

signed main() {
  int N, M;
  cin >> N >> M;

  vector<int> BOX(N+1, 1);
  BOX.at(0) = 0; //使わない
  vector<bool> fg(N+1, false);
  fg.at(1) = true; //赤が入っている可能性のある箱だけtrue

  for( int i = 0; i < M; i++ ){
    int X, Y;
    cin >> X >> Y;
    BOX.at(X)--;
    BOX.at(Y)++;
    if( fg.at(X) ) fg.at(Y) = true;
    if( BOX.at(X) == 0 ) fg.at(X) = false;
  }

  int ans = 0;
  for( int i = 1; i <= N; i++ ){
    if( fg.at(i) ) ans++;
  }

  cout << ans << endl;

}

Submission Info

Judge Result