[dfs] 백준 2606 바이러스

#include <iostream>
#include <vector>
using namespace std;
 
int ret = 0;
vector<int> v[101];
bool visited[101] = {0};
 
 
void dfs(int start);
 
int main(){
    ios_base::sync_with_stdio(false);
    
    int com_n, n;
    
    cin >> com_n >> n;
 
    for(int i = 0; i < n; i++){
        int x,y;
        cin >> x >> y;
        v[x].push_back(y);
        v[y].push_back(x);
    }
    
    dfs(1);
    
    cout << ret-1;
    
    return 0;
}
 
void dfs(int start){
    for(int i = 0; i < v[start].size(); i++){
        int tmp = v[start][i];
        
        if(visited[tmp])    continue;
        visited[tmp] = true;
        ret+=1;
        dfs(tmp);
    }
}