Forwarding Mails UVa 12442 solution - Functional graph

#include <iostream>
#include <vector>
#include <unordered_map>
#include <cmath>
#include <cstring>
#include <algorithm>
#include <set>
#include <map>
#include <queue>
#include <string>
#include <sstream>
#include <iomanip>

using namespace std;
//#define int long long
const int M = 1e9 + 7;
const int INF = 1e18 + 5;

const int N = 50005;
vector<int> g[N];
vector<int> gr[N];

//cycle
int curCycle = 0;
vector<int> cycleNodes[N];
int nodeToCycle[N];
int color[N];

// dp
int dp[N];

void dfsCycle(int node){
    color[node] = 1;
    for(int x : g[node]){
        if(color[x] == 0){
            dfsCycle(x);
        } else if(color[x] == 1){
            // cycle found  x ... node - x
            curCycle++;

            int curNode = x;
            do {
                cycleNodes[curCycle].push_back(curNode);
                nodeToCycle[curNode] = curCycle;
                curNode = g[curNode][0];
            } while(curNode != x);
        }
    }

    color[node] = 2;
}

void dfs(int node, int par){
    dp[node] = dp[par] + 1;
    for(int x : gr[node]){
        dfs(x, node);
    }
}

void solve(){
    int n; cin >> n;
    for(int i = 1; i <= n; i++){
        g[i].clear();
        gr[i].clear();

        curCycle = 0;
        cycleNodes[i].clear();
        nodeToCycle[i] = 0;
        color[i] = 0;

        dp[i] = 0;
    }

    for(int i = 1; i <= n; i++){
        int u, v; cin >> u >> v;
        g[u].push_back(v);
        gr[v].push_back(u);
    }

    for(int i = 1; i <= n; i++){
        if(color[i] == 0){
            dfsCycle(i);
        }
    }

    for(int i = 1; i <= curCycle; i++){
        for(int x : cycleNodes[i]){
            dp[x] = cycleNodes[i].size();
            for(int y : gr[x]){
                if(nodeToCycle[y] == 0){
                    dfs(y, x);
                }
            }
        }
    }

    int ans = 0;
    int ansNode = n + 1;
    for(int i = 1; i <= n; i++){
        if(dp[i] > ans){
            ans = dp[i];
            ansNode = i;
        } else if(dp[i] == ans){
            ansNode = min(ansNode, i);
        }
    }

    cout << ansNode << "\n";
}

signed main() {
//    ios_base::sync_with_stdio(false);
//    cin.tie(NULL);

    int t = 1;
    cin >> t;
    for(int i = 1; i <= t; i++){
        cout << "Case " << i << ": ";
        solve();
    }
    return 0;
}