DFS.cpp

#include <bits/stdc++.h>
using namespace std;

#define MAXN 500000

int n , m ;
int visited [MAXN] ;
vector <int> adj_list [MAXN] ;

void dfs (int x)
{
    for (int i = 0 ; i < adj_list[x].size() ; i++)
    {
        int v = adj_list[x][i] ;

        if(visited[v] == -1)
        { 
            visited[v] = visited[x] ;
            dfs(v) ;
        }
    }
}
void initialize ()
{
    for (int i = 1 ; i <= n ; i++) 
    {
        visited[i] = -1 ; 
    }
}
int main ()
{
    int a , b ;

    cin >> n >> m ;

    initialize();

    for (int i = 1 ; i <= m ; i++)
    {
        cin >> a >> b ;

        adj_list[a].push_back(b) ;
        adj_list[b].push_back(a) ;
    }

    dfs(1) ;

    return 0;
}