# Number of Connected Components in an Undirected Graph -- LeetCode

Datetime:2016-08-23 01:20:14         Topic: LeetCode          Share        Original >>

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` .

Note:

You can assume that no duplicate edges will appear in  `edges` . Since all edges are undirected,  `[0, 1]` is the same as  `[1, 0]` and thus will not appear together in  `edges` .

``` 1 class Solution {
2 public:
3     int getFather(vector<int>& father, int i) {
4         if (father[i] == i) return i;
5         father[i] = getFather(father, father[i]);
6         return father[i];
7     }
8     void merge(vector<int>& father, int i, int j) {
9         int fatherI = getFather(father, i);
10         int fatherJ = getFather(father, j);
11         father[fatherJ] = fatherI;
12     }
13     int countComponents(int n, vector<pair<int, int>>& edges) {
14         vector<int> father;
15         for (int i = 0; i < n; i++) father.push_back(i);
16         for (int i = 0, n = edges.size(); i < n; i++)
17             merge(father, get<0>(edges[i]), get<1>(edges[i]));
18         unordered_set<int> unions;
19         for (int i = 0; i < n; i++) unions.insert(getFather(father, i));
20         return unions.size();
21     }
22 };
```