Construct Binary Tree from Inorder and Postorder Traversal
Given two integer arrays inorder and postorder, where inorder is the inorder traversal of a binary tree and postorder is the postorder traversal of the same tree, construct and return the binary tree.
You may assume that all values in the tree are unique.
Example 1
Input
inorder = [9,3,15,20,7] postorder = [9,15,7,20,3]
Output
[3,9,20,15,7]
Explanation
The last element of postorder is 3, so 3 is the root. In inorder, 3 separates the left subtree [9] from the right subtree [15,20,7].
Example 2
Input
inorder = [-1] postorder = [-1]
Output
[-1]
Explanation
There is only one node, so it becomes the root of the tree.
Constraints
Hints:
Hint 1
The last element of postorder is always the root of the current subtree.
Hint 2
Find the root in inorder to divide the remaining elements into the left and right subtrees, then recursively construct both parts.
Author & Technical Reviewer
Technically reviewed by: ExamAdda Technical Review Team
Technical Reviewers, ExamAdda
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Published
Aug 18, 2026
Last updated
Aug 19, 2026
Content Verification Methodology
Definitions and complexity claims were checked against authoritative computer-science references. Code examples were compiled and tested with standard, boundary and edge-case inputs.
Expected Output