Construct Binary Search Tree from Preorder Traversal

main.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 bstFromPreorder(self, preorder: List[int]) -> TreeNode:
        root = TreeNode(preorder[0])
        
        def insert(val):
            curr = root
            while True:
                if val < curr.val:
                    # Insert into left subtree.
                    if curr.left is None:
                        curr.left = TreeNode(val)
                        break
                    else:
                        curr = curr.left
                else:
                    # Insert into right subtree.
                    if curr.right is None:
                        curr.right = TreeNode(val)
                        break
                    else:
                        curr = curr.right

        for val in preorder[1:]:
            insert(val)

        return root