Tree_Traversals_In_Pre_Post_Order.py

# Program to traverse given tree in pre-order, in-order and post-order fashion


class TreeNode:
    def __init__(self, val):
        self.val = val
        self.left = None
        self.right = None


class Tree:
    def __init__(self, root):
        self.root = TreeNode(root)

    def inorder_traversal(self, node, path):
        if node:
            path = self.inorder_traversal(node.left, path)
            path += str(node.val) + ' '
            path = self.inorder_traversal(node.right, path)

        return path

    def preorder_traversal(self, node, path):
        if node:
            path += str(node.val) + ' '
            path = self.preorder_traversal(node.left, path)
            path = self.preorder_traversal(node.right, path)

        return path

    def postorder_traversal(self, node, path):
        if node:
            path = self.postorder_traversal(node.left, path)
            path = self.postorder_traversal(node.right, path)
            path += str(node.val) + ' '

        return path

# Creating a tree of the following structure:-

#      1
#    /   \
#   2     3
#  / \   / \
# 4   5 6   7

tree = Tree(1)

tree.root.left = TreeNode(2)
tree.root.right = TreeNode(3)

tree.root.left.left = TreeNode(4)
tree.root.left.right = TreeNode(5)
tree.root.right.left = TreeNode(6)
tree.root.right.right = TreeNode(7)

# In-Order Traversal :- left -> root -> right

print(tree.inorder_traversal(tree.root, ''))
# Expected Output:- 4 2 5 1 6 3 7

# Pre-Order Traversal :- root -> left -> right

print(tree.preorder_traversal(tree.root, ''))
# Expected Output:- 1 2 4 5 3 6 7

# Post-Order Traversal :- left -> right -> root

print(tree.postorder_traversal(tree.root, ''))
# Expected Output:- 4 5 2 6 7 3 1