LC 1008 [M] Construct Binary Search Tree from Preorder Traversal - ALawliet/algorithms GitHub Wiki

# 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])
        stack = [root]
        
        for x in preorder[1:]:
            node = TreeNode(x)
            
            if node.val < stack[-1].val:
                stack[-1].left = node
            else:
                while stack and node.val > stack[-1].val:
                    last = stack.pop()
                last.right = node
                
            stack.append(node)
            
        return root