105. Construct Binary Tree from Preorder and Inorder Traversal.py

# Definition for a binary tree node.
class TreeNode:
    def __init__(self, val=0, left=None, right=None):
        self.val = val
        self.left = left
        self.right = right
        
class Solution:
    def buildTree(self, preorder: List[int], inorder: List[int]) -> Optional[TreeNode]:
        
        # In Order - L-N-R
        # Pre Order - N-L-R

        if not preorder or not inorder: return None

        root = TreeNode(preorder[0])
        mid = inorder.index(root.val)

        root.left = self.buildTree(preorder[1:mid+1],inorder[:mid])
        root.right = self.buildTree(preorder[mid+1:],inorder[mid+1:]) 

        return root