Construct Binary Tree from Inorder and Postorder Traversal

Moderate

0/80

Average time to solve is 25m

Contributed by

33 upvotes

Problem statement

You are given arrays 'inOrder' and 'postOrder', which represent 'inorder' traversal and 'postorder' traversal of a 'Binary Tree' respectively.

Construct a 'Binary Tree' represented by the given arrays and return it's head.

Note:

Assume that the Binary Tree contains only unique elements.

Example:

Input: 'inOrder' = [9, 3, 15, 20, 7], 'postOrder' = [9, 15, 7, 20, 3]

Output:
We get the following binary tree from Inorder and Postorder traversal:

Detailed explanation ( Input/output format, Notes, Images )

Input Format

The first line of each test case contains an integer 'n' which represents the number of nodes in the Binary Tree.

The next line of each test case contains 'n' single space-separated integers, representing the Postorder traversal of the Binary Tree.

The next line of each test case contains 'n' single space-separated integers, representing the Inorder traversal of the Binary Tree.

Output Format :

Return the head of the binary tree constructed.
The level order traversal of the Binary Tree is printed.

Note:

You do not need to print anything; it has already been taken care of. Just implement the given function.

Sample Input 1:

7
4 5 2 6 7 3 1
4 2 5 1 6 3 7

Output on console:

1 2 3 4 5 6 7

Explanation for Sample Output 1:

We get the following Binary Tree from the given Inorder and Postorder traversal:

Sample Input 2:

6
2 9 3 6 10 5
2 6 3 9 5 10

Sample Output 2:

5 6 10 2 3 9

Explanation for Sample Output 2:

We get the following Binary Tree from the given Inorder and Postorder traversal:

Expected Time Complexity:

Try to solve this in O(n).

Constraints :

1 <= 'n' <= 10000
1 <=  'inOrder[i]' , ‘postOrder[i]’ <= 100000  

Time Limit: 1 second

Console