Tunnelit

#include <iostream>
#include <vector>
#include <queue>
#include <algorithm>
#include <unordered_set>
#define ll long long
using namespace std;
int n, k, o,m, p, r, a[101010], b[101010], c[1010][1010], z[101010];
vector<int> v[101010];
vector<pair<int,int>> lh;
queue<int> q;
unordered_set<int> ses[101010];
vector<int> w;
void haku2(int s) {
	//cout << "haussa << " << s << endl;
	for (auto u: v[s]) {
		if (ses[s].find(u) != ses[s].end()) continue;
		//c[s][u] = 1;
		ses[s].insert(u);
		a[u]--;
		b[s]--;
		haku2(u);
		break;
	}
}
void haku1(int s) {
	if (z[s]) return;
	z[s] = 1;
	for (auto u: v[s]) {
		haku1(u);
	}
	w.push_back(s);
}
int main() {
	cin >> n >> m;
	for (int i = 0; i < m; i++) {
		cin >> o >> p;
		a[o]++;
		b[p]++;
		v[o].push_back(p);
	}
	for (int i = 1; i <= n; i++) {
		haku1(i);
	}
	reverse(w.begin(), w.end());
	//cout << "koko" << w.size() << endl;
	for (auto u: w) {
		//cout << u << "lähtee tästä"<<  endl;
		while (a[u] > 0) {
			//cout << u << endl;
			haku2(u);
			r++;
			a[u]--;
		}
	}
	cout << r << endl;
}

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