Challenge: Implement Breadth-First Graph Traversal

Problem statement

You have to implement the breadth-first traversal in Python.

To solve this problem, the previously implemented Graph class is already prepended.

Input

A graph represented as an adjacency list and a starting vertex

Output

A string containing the vertices of the graph listed in the correct order of traversal

Sample input

Graph:

Vertex	Edges
0	2, 1
1	4, 3
2	None
3	None
4	None

Source: 0

Sample output

result = "02143" 
or
result = "01234"

Traversal strategy: print the right child first and then, the left child.