Construct Binary Tree from Preorder and Inorder Traversal - Leetcode 105 - Python

Construct Binary Tree from Preorder and Inorder Traversal

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.

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

class Solution:
    def buildTree(self, p: List[int], i: List[int]) -> Optional[TreeNode]:
        if not p or not i:
            return None
        
        # p = [3,9,20,15,7]
        # i = [9,3,15,20,7] 
        
        root = TreeNode(p[0])
        mid = i.index(p[0]) # mid = 1
        
        root.left = self.buildTree(p[1:mid+1],i[:mid])
        root.right = self.buildTree(p[mid+1:],i[mid+1:])
        
        return root

Explaination :

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