Breadth-First Search Tree

OPEN: a VISITED: nil
OPEN: b c d e VISITED: a
OPEN: c d e f g VISITED: a b
OPEN: d e f g h VISITED: a b c
OPEN: e f g h i j k l VISITED: a b c d
OPEN: f g h i j k l VISITED: a b c d e
OPEN: g h i j k l VISITED: a b c d e f
OPEN: h i j k l VISITED: a b c d e f g
OPEN: i j k l VISITED: a b c d e f g h
OPEN: j k l GOAL VISITED: a b c d e f g h i
OPEN: k l GOAL VISITED: a b c d e f g h i j
OPEN: l GOAL VISITED: a b c d e f g h i j k
OPEN: GOAL VISITED: a b c d e f g h i j k l
OPEN: VISITED: a b c d e f g h i j k l GOAL