import java.util.*;

public class numOfComp {

// 跟 count number of islands 很像

public int count(int n, int[][] edges){

// build the graph

Map<Integer, List<Integer>> map = new HashMap<>();

for(int i = 0; i < n; i++) map.put(i, new ArrayList<>());

for(int[] edge : edges){

map.get(edge[0]).add(edge[1]);

map.get(edge[1]).add(edge[0]);

}

Set<Integer> visited = new HashSet<>();

int res = 0;

for(int i = 0; i < n; i++){

if(!visited.contains(i)){

res ++;

dfs(map, visited, i);

}

}

return res;

}

private void dfs(Map<Integer, List<Integer>> map, Set<Integer> visited, int i){

if(visited.contains(i)) return;

visited.add(i);

for(int child : map.get(i)){

dfs(map, visited, child);

}

}

}