In each line, the front of the queue is at the left.
A B C C D D E F E F F G G H I H I I
(a) Preorder:
A B D H E I C F J K G
(b) Postorder:
H D I E B J K F G C A
(c) Level-order:
A B C D E F G H I J K
(d) In-order:
D H B I E A J F K C G
