Number of Connected Components in an Undirected Graph

 1 public class Solution {
 2     private int[] parent;
 3     public int countComponents(int n, int[][] edges) {
 4         if (edges.length == 0) {
 5             return n;
 6         }
 7         parent = new int[n];
 8         for (int i = 0; i < n; i++) {
 9             parent[i] = i;
10         }
11
12         for (int i = 0; i < edges.length; i++) {
13             int aIndex = findParent(edges[i][0]);
14             int bIndex = findParent(edges[i][1]);
15
16             if (aIndex > bIndex) {
17                 parent[aIndex] = bIndex;
18             } else if (bIndex > aIndex) {
19                 parent[bIndex] = aIndex;
20             }
21         }
22
23         int result = 0;
24         for (int i = 0; i < n; i++) {
25             if (parent[i] == i) {
26                 result++;
27             }
28         }
29         return result;
30     }
31
32     private int findParent(int x) {
33         while (x != parent[x]) {
34             parent[x] = parent[parent[x]];
35             x = parent[x];
36         }
37         return x;
38     }
39 }