Tunnels

#include<bits/stdc++.h>

#define F first
#define S second
#define ll long long
#define ull unsigned long long
#define pb push_back
using namespace std;
ll n, m, used[200000], r, d[200000], c, s;
vector < ll > k;
set < ll > g[200000];
ll dp[200000], f[200000], b[200000], ans;
int dfs(int v){
    if (dp[v] != 0) return dp[v];
    for (auto u: g[v]){
        if (dfs(u) + 1 > dp[v]){
            f[v] = u;
            dp[v] = dfs(u) + 1;
        }
    }
    return dp[v];
}
void dfs1(int v)
{
    if (f[v] == -1) return;
    g[v].erase(f[v]);
    b[f[v]]--;
    dfs1(f[v]);
}
int main()
{
    ios_base::sync_with_stdio(false);
    cin.tie(NULL);
    cin >> n >> m;
    for (int i = 1; i <= m; i++){
        int u, v;
        cin >> u >> v;
        g[u].insert(v);
        b[v]++;
    }
    for (int kk = 1; kk <= n; kk++)
        for (int i = 1; i <= n; i++)
            if (b[i] == 0){
            for (int j = 1; j <= n; j++){
                dp[j] = 0;
                f[j] = -1;
            }
            dfs(i);
            dfs1(i);
            if (f[i] != -1)
            ans++;
        }
    cout << ans;
}

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