Challenge: Implement Depth First Search

Problem statement

You have to implement the Depth First Search algorithm on a directed graph using the data structures which we have implemented in the previous sections.

Note: Your solution should work for both connected and unconnected graphs.

Input

A directed graph in the form of 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	None
1	3, 2
2	5, 4
3	6
4	None
5	None
6	None

Sample output

"1245360" or "1362540"