題目：
題解：
class Solution:def buildTree(self, preorder: List[int], inorder: List[int]) -> TreeNode:if not preorder:return Noneroot = TreeNode(preorder[0])stack = [root]inorderIndex = 0for 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 += 1node.right = TreeNode(preorderVal)stack.append(node.right)return root
