Tunnels

#include <iostream>
#include <algorithm>
#include <set>
using namespace std;
set <int> s[100002];
set <int>::iterator it;
int q[100002];
int n,m;
void dfs(int gag,int ngag){
    if(ngag!=gag){
        m--;
        it=s[ngag].lower_bound(gag);
        s[ngag].erase(it);
        q[gag]--;
    }
    for(set <int> ::iterator it=s[gag].begin();it!=s[gag].end();it++){
        int to=*it;
        dfs(to,gag);
        return;
    }
}
int main(){
    cin>>n>>m;
    for(int i=0;i<m;i++){
        int j,k;
        cin>>j>>k;
        s[j].insert(k);
        q[k]++;
    }
    int ans=0;
    while(m>0){
        ans++;
        for(int j=1;j<=n;j++){
            if(q[j]==0 && s[j].size()>0){
                dfs(j,j);
                break;
            }
        }
    }
    cout<<ans<<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: TIME LIMIT EXCEEDED

Test 12

Group: 3

Verdict: TIME LIMIT EXCEEDED

Test 13

Group: 3

Verdict: TIME LIMIT EXCEEDED

Test 14

Group: 3

Verdict: TIME LIMIT EXCEEDED

Test 15

Group: 3

Verdict: TIME LIMIT EXCEEDED