105. Construct Binary Tree from Preorder and Inorder Traversal

Medium

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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.

class Solution:
    def buildTree(self, preorder: List[int], inorder: List[int]) -> Optional[TreeNode]:
        if inorder:
            index = inorder.index(preorder.pop(0))
            root = TreeNode(inorder[index])
            root.left = self.buildTree(preorder, inorder[:index])
            root.right = self.buildTree(preorder, inorder[index+1:])
            return root