Print Depth First Traversal using recursion.

DepthFirstTraversalUsingRecursion.cpp

void print_depth_first_traversal(GraphNode *node) {
    if (is_visited(node)) {
        return;
    }
    mark_visited(node);

    for (GraphNode *neighbor : node->neighbors) {
        print_depth_first_traversal(neighbor);
    }

    print(node->value);
}