Submission #826139

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Source Code Expand

#include <iostream>
#include <set>
#include <vector>

using namespace std;

int main(int argc, char* argv[]) {
  int N, M;
  cin >> N >> M;

  vector<int> X(M), Y(M), Box(M);
  for (int i = 0; i < M; i++) {
    int x, y;
    cin >> x >> y;
    x--; y--;
    X[i] = x; Y[i] = y;
    Box[i] = 1;
  }

  set<int> red;
  red.insert(0);
  for (int i = 0; i < M; i++) {
    int from = X[i], to = Y[i];
    for (set<int>::iterator itr = red.begin();
	 itr != red.end(); itr++) {
      if (*itr == from) {
	red.insert(to);
	if (Box[from] == 1) {
	  red.erase(itr);
	}
      }
    }
    Box[to]++;
    Box[from]--;
  }

  cout << red.size() << endl;
  return 0;
}

Submission Info

Judge Result