Tunnels

#include <iostream>
#include <set>
#include <algorithm>
using namespace std;

const int N = 100000;
vector <int> G[N + 7];
int odw[N + 7];
int d[N + 7];
int d2[N + 7];
int n, m;
int wynik = 0;
int nwyn;

void dfs(int v) {
	odw[v] = 1;
	nwyn += max(d[v], 0);
	for(auto u : G[v]) {
		if(!odw[u]) {
			dfs(u);
		}
	}
}

int main() {
	ios_base::sync_with_stdio(0);
	cin >> n >> m;
	for(int i = 0; i < m; ++i) {
		int a, b;
		cin >> a >> b;
		d[a]++;
		d[b]--;
		d2[a]++;
		d2[b]++;
		G[a].push_back(b);
		G[b].push_back(a);
	}
	
	for(int i = 1; i <= n; ++i) {
		if(!odw[i] && d2[i] > 0) {
			nwyn = 0;
			dfs(i);
			if(nwyn == 0) nwyn++;
			wynik += nwyn;
		}
	}
	cout << wynik << endl;
	return 0;
}

Test 1

Group: 1

Verdict: ACCEPTED

Test 2

Group: 1

Verdict: ACCEPTED

Test 3

Group: 1

Verdict: ACCEPTED

Test 4

Group: 1

Verdict: ACCEPTED

Test 5

Group: 1

Verdict: ACCEPTED

Test 6

Group: 2

Verdict: ACCEPTED

Test 7

Group: 2

Verdict: ACCEPTED

Test 8

Group: 2

Verdict: ACCEPTED

Test 9

Group: 2

Verdict: ACCEPTED

Test 10

Group: 2

Verdict: ACCEPTED

Test 11

Group: 3

Verdict: ACCEPTED

Test 12

Group: 3

Verdict: ACCEPTED

Test 13

Group: 3

Verdict: ACCEPTED

Test 14

Group: 3

Verdict: ACCEPTED

Test 15

Group: 3

Verdict: ACCEPTED