Depth-First Search

The Depth-First Search is a recursive algorithm that finds if there is a path from one node to another.

This algorithm searches for the node's children first before going to the neighbours.

To avoid the algorithm to run in circle infinitely, a flag should indicate if the node has been visited once. The algorithm concludes there is a path between two nodes A and B if one of the node's A children has a path to node B. And, obviously each node has a path to itself.