Binary tree traversals(Divide and Conquer)

1. Binary Tree Traversals
Divide-and-Conquer Technique

2. Tree Traversal
 Also known as tree search and walking the tree
 Refers to the process of visiting each node in a tree data
structure exactly once
structure exactly once

3. Tree Traversal Technique
 Based on the order in which the nodes are visited,
 Inorder traversal L-Ro-R
 Preorder traversal Ro-L-R
 Postorder traversal L-R-Ro

4. Inorder traversal
Inorder(root)
 Traverse the left sub-tree,
(recursively call inorder(root -> left)
(recursively call inorder(root -> left)
 Visit and print the root node.
 Traverse the right sub-tree,
(recursively call inorder(root -> right)
Inorder: d, g, b, e, a, f, c

5. Preorder traversal
Preorder(root)
 Visit and print the root node.
 Traverse the left sub-tree,
(recursively call inorder(root -> left)
 Traverse the right sub-tree,
(recursively call inorder(root -> right)
Preorder: a, b, d, g, e, c, f

6. Postorder traversal
Preorder(root)
 Traverse the left sub-tree,
(recursively call inorder(root -> left)
(recursively call inorder(root -> left)
 Traverse the right sub-tree,
(recursively call inorder(root -> right)
 Visit and print the root node.
Postorder: g, d, e, b, f, c, a

8. Pre-order (node access at position
red ):
F, B, A, D, C, E, G, I, H
In-order (node access at position
In-order (node access at position
green):
A, B, C, D, E, F, G, H, I
Post-order (node access at position
blue):
A, C, E, D, B, H, I, G, F

9. External and Internal Node
 Number of external
nodes x is
always 1 more than
the number of
the number of
internal nodes n:
x = n + 1