OBI Famílias de Troia

#include <bits/stdc++.h>
#define MAXN 50010

using namespace std;

vector<int> grafo[MAXN];
int marc[MAXN];

void dfs (int v){
    marc[v] = 1;
    for (int i = 0; i < grafo[v].size(); i++){
        int viz = grafo[v][i];
        if (marc[viz] == 0){
            dfs(viz);
        }
    }
}

int main (){
    int n, m;
    scanf("%d %d", &n, &m);
    //LEITURA DO GRAFO
    for (int i = 0; i < m; i++){
        int a, b; scanf("%d %d", &a, &b);
        grafo[a].push_back(b);
        grafo[b].push_back(a);
    }
    //CONTANDO AS COMPONENTES CONEXAS
    int cont = 0;
    for (int i = 1; i <= n; i++){
        if (marc[i] == 0){
            dfs(i);
            cont++;
        }
    }
    printf("%d", cont);
}