Given
n
nodes labeled from 0
to n - 1
and a list of undirected edges (each edge is a pair of nodes), write a function to find the number of connected components in an undirected graph.
Example 1:
0 3 | | 1 --- 2 4
Given
n = 5
and edges = [[0, 1], [1, 2], [3, 4]]
, return 2
.
Example 2:
0 4 | | 1 --- 2 --- 3
Given
n = 5
and edges = [[0, 1], [1, 2], [2, 3], [3, 4]]
, return 1
.
Code:
public class Solution {
public int countComponents(int n, int[][] edges) {
if (n <= 1)
return n;
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 count = 0;
for (int i = 0; i < n; i++) {
if (visited.add(i)) {
dfsVisit(i, map, visited);
count++;
}
}
return count;
}
private void dfsVisit(int i, Map<Integer, List<Integer>> map, Set<Integer> visited) {
for (int j : map.get(i)) {
if (visited.add(j))
dfsVisit(j, map, visited);
}
}
}
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