Tunnels

input/code.cpp: In function 'int main()':
input/code.cpp:48:25: 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:50:38: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
       int u, v; scanf("%d%d", &u, &v);
                                      ^

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

const int MAXN = 1e5;

int N, M;
deque<int> G[MAXN + 10];

vector<int> in[MAXN + 10];
int out[MAXN + 10];
int pos[MAXN + 10];
int ind[MAXN + 10];

bool vis[MAXN + 10];

void top_sort() {
   queue<int> q;
   int ii = N;
   for(int u = 1; u <= N; u++) {
      if(out[u] == 0) {
         q.push(u);
      }
   }
   while(!q.empty()) {
      int v = q.front(); q.pop();
      ind[ii] = v; pos[v] = ii;
      --ii;
      for(int u : in[v]) {
         out[u]--;
         if(out[u] == 0) q.push(u);
      }
   }
   for(int u = 1; u <= N; u++) {
      out[u] = G[u].size();
      sort(G[u].begin(), G[u].end(),
         [&](int u, int v) { return pos[u] < pos[v]; });
   }
}

bool work(int u) {
   if(G[u].size() == 0) return false;
   work(G[u][0]);
   G[u].pop_front();
   return true;
}

int main() {
   scanf("%d%d", &N, &M);
   for(int i = 0; i < M; i++) {
      int u, v; scanf("%d%d", &u, &v);
      out[u]++;
      G[u].push_back(v);
      in[v].push_back(u);
   }
   top_sort();
   int res = 0;
   for(int i = 1; i <= N; i++) {
      while(work(ind[i])) {
         res++;
      }
   }
   printf("%d\n", res);
}

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