323. Number of Connected Components in an Undirected Graph

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:

Input: 

n = 5

 and 
edges = [[0, 1], [1, 2], [3, 4]]

     0          3
     |          |
     1 --- 2    4 
Output: 

2

Example 2:

Input: 

n = 5

 and 
edges = [[0, 1], [1, 2], [2, 3], [3, 4]]

     0           4
     |           |
     1 --- 2 --- 3
Output:  

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 .