Tunnels

input/code.cpp: In function 'int main()':
input/code.cpp:28:24: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
  scanf("%d %d", &n, &m);
                        ^
input/code.cpp:32:25: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
   scanf("%d %d", &x, &y);
                         ^

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

// why am I so weak

int n, m;
bool used[100055];
vector<int> g[100055], vs;

void dfs(int v) {
	if (used[v]) return;

	used[v] = true;

	for (auto u : g[v]) {
		dfs(u);
	}

	vs.push_back(v);
}
void rdfs(int v) {
	if (g[v].empty()) return;

	rdfs(g[v].back());
	g[v].pop_back();
}
int main() {
	scanf("%d %d", &n, &m);

	while (m--) {
		int x, y;
		scanf("%d %d", &x, &y);
		x--, y--;

		g[x].push_back(y);
	}

	for (int i = 0; i < n; i++) if (!used[i]) {
		dfs(i);
	}


	int res = 0;

	for (int i = n - 1; i >= 0; i--) {
		int v = vs[i];
		while (!g[v].empty()) {
			res++;
			rdfs(g[v].back());
			g[v].pop_back();
		}
	}

	cout << res << 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