Question

use postorder and inorder tree traversals to make preorder traversal.

#!/usr/bin/env python3

# encoding: UTF-8

"""Turning in-order and post-order tree traversals into pre-order"""

def get_preorder(inorder: str, postorder: str) -> str:

"""Return pre-order traversal of a tree based on its in-order and post-order traversals"""

#Complete the following function

#raise NotImplementedError

Answer 1

For the above program, we need to have the following things into consideration.

1. We need to find the postorder of the above-given tree from the inorder and preorder.
2. Then we need to print the post order

Following is the python code:

# Printing the post order
post_order = []
def postorder(inorder, preorder, n):
    if preorder[0] in inorder:
        root = inorder.index(preorder[0])

    if root != 0:  # left subtree exists
        postorder(inorder[:root],
                       preorder[1:root + 1],
                       len(inorder[:root]))

    if root != n - 1:  # right subtree exists
        postorder(inorder[root + 1:],
                       preorder[root + 1:],
                       len(inorder[root + 1:]))

    post_order.append(preorder[0])


def get_preorder(inorder, preorder):
    postorder(inorder, preorder, len(inorder))


# Driver Code
inorder = [4, 2, 5, 1, 3, 6];
preorder = [1, 2, 4, 5, 3, 6];
n = len(inorder)
print("Postorder traversal ")
get_preorder(inorder, preorder)
print(post_order)

Following is the snippet of the above program .:

The Output of the above program.

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