Tunnels

#include <bits/stdc++.h>
// iostream is too mainstream
#include <cstdio>
// bitch please
#include <iostream>
#include <algorithm>
#include <cstdlib>
#include <vector>
#include <set>
#include <map>
#include <queue>
#include <stack>
#include <list>
#include <cmath>
#include <iomanip>
#include <time.h>
#define dibs reserve
#define OVER9000 1234567890
#define ALL_THE(CAKE,LIE) for(auto LIE =CAKE.begin(); LIE != CAKE.end(); LIE++)
#define tisic 47
#define soclose 1e-8
#define chocolate win
// so much chocolate
#define patkan 9
#define ff first
#define ss second
#define abs(x) ((x < 0)?-(x):x)
#define uint unsigned int
#define dbl long double
#define pi 3.14159265358979323846
using namespace std;
// mylittledoge

#ifdef DONLINE_JUDGE
	// palindromic tree is better than splay tree!
	#define lld I64d
#endif

/*
	Spurdo Spärde :DDDD
	SPEDE BEARD
	PEDRO SPORA
	PURJO PORE
	SPEARMINT PUDDING
	SPORO LORO
	PUDRO BARDE
	BENIS XDDDD :DDD XD
*/

int main() {
	cin.sync_with_stdio(0);
	cin.tie(0);
	cout << fixed << setprecision(10);

	int N,M;
	cin >> N >> M;
	vector<int> D(N,0);
	vector< vector<int> > Gi(N),Go(N);
	for(int i =0; i < M; i++) {
		int a,b;
		cin >> a >> b;
		a--, b--;
		D[b]++;
		Gi[a].push_back(b);
		Go[b].push_back(a);}

	queue<int> q;
	for(int i =0; i < N; i++) if(D[i] == 0) q.push(i);
	int ans =0;
	vector<int> pths_in(N,0);
	while(!q.empty()) {
		ans +=max(0,(int)Gi[q.front()].size()-(int)Go[q.front()].size());
		ALL_THE(Gi[q.front()],it) {
			D[*it]--;
			if(D[*it] == 0) q.push(*it);}
		q.pop();}

	cout << ans << "\n";
	return 0;}

// look at my code
// my code is amazing

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