So tree traversals...
Tree structure
-------------------------------------
Root
(A)
-------------------------------------
L1
(B)(C)
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L2
(D)(E)(F)(G)
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L3
(H)(I)(J)(K)
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DFS in order traversal
H D I B J E K A F C G
-------------------------------------
DFS pre order traversal
A B D H I E J K C F G
-------------------------------------
DFS post order traversal
B D H I E J K C F G A