Question

[Python]

Construct Tree Using Inorder and Preorder

Given Preorder and Inorder traversal of a binary tree, create the binary tree associated with the traversals.You just need to construct the tree and return the root.

Note: Assume binary tree contains only unique elements.

Input format :

Line 1 : n (Total number of nodes in binary tree)

Line 2 : Pre order traversal

Line 3 : Inorder Traversal

Output Format :

Elements are printed level wise, each level in new line (separated by space).

Sample Input :

12
1 2 3 4 15 5 6 7 8 10 9 12
4 15 3 2 5 1 6 10 8 7 9 12

Sample Output :

1 
2 6 
3 5 7 
4 8 9 
15 10 12

Solution:

import queue
class BinaryTreeNode:
def __init__(self, data):
self.data = data
self.left = None
self.right = None

def buildTreePreOrder(preorder, inorder):
# Given Preorder and Inorder traversal of a binary tree, create the binary
# tree associated with the traversals.You just need to construct the tree
# and return the root. For 12 Nodes with following input:
# preOrder: 1 2 3 4 15 5 6 7 8 10 9 12
# inOrder: 4 15 3 2 5 1 6 10 8 7 9 12
#############################
# PLEASE ADD YOUR CODE HERE #
#############################
pass

def printLevelATNewLine(root):
# Given a binary tree, print the level order traversal. Make sure each level
# start in new line.
if root==None:
return
inputQ = queue.Queue()
outputQ = queue.Queue()
inputQ.put(root)
while not inputQ.empty():
while not inputQ.empty():
curr = inputQ.get()
print(curr.data, end=' ')
if curr.left!=None:
outputQ.put(curr.left)
if curr.right!=None:
outputQ.put(curr.right)
print()
inputQ, outputQ = outputQ, inputQ

# Main
n=int(input())
preorder = [int(i) for i in input().strip().split()]
inorder = [int(i) for i in input().strip().split()]
root = buildTreePreOrder(preorder, inorder)
printLevelATNewLine(root)

Code looks like this in editor:

In [ ]: import queue class Binary TreeNode: definit__(self, data): self.data = data self.left = None self.right = None def buildTreePreOrder(preorder, inorder):| pass def printLevelATNewLine(root): # Given a binary tree, print the level order traversal. Make sure each level # start in new Line. if root==None: return input = queue. Queue () output = queue. Queue () input.put(root) while not inputq.empty(): while not input.empty(): curr = input.get() print(curr.data, end=' ') if curr.left !=None: output.put(curr.left) if curr.right! =None: outputq.put(curr.right) print() input, output = outputo, input # Main n=int(input) preorder = [int(i) for i in input().strip().split()] inorder = [int(i) for i in input().strip().split() root = buildTreePreOrder (preorder, inorder) printLevelATNewLine(root)

Answer 1

def ConstructTree(inOrder, preOrder, inStrt, inEnd):

     if (inStrt > inEnd) :

        return None

CurrentNode = Node(preOrder[ConstructTree.preIndex])

ConstructTree.preIndex += 1

    if inStrt == inEnd :

        return CurrentNode

    inIndex = search(inOrder, inStrt, inEnd, tNode.data)

CurrentNode.left = ConstructTree(inOrder, preOrder, inStrt, inIndex-1)

CurrentNode.right = ConstructTree(inOrder, preOrder, inIndex + 1, inEnd)

  return currentNode

Hope this code helps you. For better Understanding try to dry run. Please give an upvote if it does.