“PHP is a minor evil perpetrated and created by incompetent amateurs, whereas Perl is a great and insidious evil perpetrated by skilled but perverted professionals.” (Jon Ribbens)
We start with the generic visitation algorithm and using a queue to represent S we obtain breadth-first visitation (Breadth First Search or BFS).
Nodes are visited by levels, first root, then children of the root, then children of the children.
algorithm BFS(node r)
Queue C
C.enqueue(r)
while not C.isEmpty() do
u ← C.dequeue()
if u ≠ null then
visit(u)
C.enqueue(leftChildOf(u))
C.enqueue(rightChildOf(u))