0105: Construct Binary Tree from Preorder and Inorder Traversal

Problem Statement

Given two integer arrays preorder and inorder where preorder is the preorder traversal of a binary tree and inorder is the inorder traversal of the same tree, construct and return the binary tree.

Example 1:

Input: preorder = [3,9,20,15,7], inorder = [9,3,15,20,7]
Output: [3,9,20,null,null,15,7]

Example 2:

Input: preorder = [-1], inorder = [-1]
Output: [-1]

Constraints:

  • 1 <= preorder.length <= 3000
  • inorder.length == preorder.length
  • -3000 <= preorder[i], inorder[i] <= 3000
  • preorder and inorder consist of unique values.
  • Each value of inorder also appears in preorder.
  • preorder is guaranteed to be the preorder traversal of the tree.
  • inorder is guaranteed to be the inorder traversal of the tree.

Code Solution

class Solution:
    def buildTree(self, preorder, inorder):
	    
        def rec(po, io):
            if not po:
                return None
            ix = io.index(po[0])
            return TreeNode(
                po[0],
                rec(po[1:1+ix], io[0:ix]),
                rec(po[1+ix:], io[1+ix:])
            )
        
        return rec(preorder, inorder)