Challenge: Implement Depth First Search

Problem Statement

You have to implement the Depth First Search algorithm on a graph.

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

Input

A graph in the form of an adjacency list

Note: You can start the traversal from any vertex.

Output

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

Sample Input

Graph:

Vertex	Edges
1	3, 2
2	5, 4
3	6
4	null
5	null
6	null

Sample Output

"124536" or "136254"