# Question

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.

# Solution

```
from collections import defaultdict, deque
class Solution(object):
def countComponents(self, n, edges):
"""
:type n: int
:type edges: List[List[int]]
:rtype: int
"""
class Graph(object):
def __init__(self, vertices):
self.graph = defaultdict(list)
self.V = vertices
def addEdge(self, u, v):
self.graph[u].append(v)
self.graph[v].append(u)
def connectedComponents(self):
unvisited = set(range(self.V))
queue = deque()
count = 0
while len(unvisited) > 0:
count += 1
v = next(iter(unvisited))
unvisited.remove(v)
queue.append(v)
while len(queue) > 0:
v = queue.popleft()
for w in self.graph[v]:
if w in unvisited:
unvisited.remove(w)
queue.append(w)
return count
graph = Graph(n)
for e in edges:
graph.addEdge(e[0], e[1])
return graph.connectedComponents()
```