题目：

题解：

class Solution:
    def buildTree(self, preorder: List[int], inorder: List[int]) -> TreeNode:
        if not preorder:
            return None

        root = TreeNode(preorder[0])
        stack = [root]
        inorderIndex = 0
        for i in range(1, len(preorder)):
            preorderVal = preorder[i]
            node = stack[-1]
            if node.val != inorder[inorderIndex]:
                node.left = TreeNode(preorderVal)
                stack.append(node.left)
            else:
                while stack and stack[-1].val == inorder[inorderIndex]:
                    node = stack.pop()
                    inorderIndex += 1
                node.right = TreeNode(preorderVal)
                stack.append(node.right)

        return root