需要从inOrder和preOrder返回postOrder树

class TreeNode:
    def __init__(self, val=0, left=None, right=None):
        self.val = val
        self.left = left
        self.right = right

def buildTree(inOrder, preOrder):
    if not inOrder or not preOrder:
        return None

    # 根据preOrder确定根节点
    root_val = preOrder[0]
    root = TreeNode(root_val)

    # 在inOrder中找到根节点的位置
    root_index = inOrder.index(root_val)

    # 划分左子树和右子树的inOrder和preOrder
    left_inOrder = inOrder[:root_index]
    right_inOrder = inOrder[root_index+1:]
    left_preOrder = preOrder[1:root_index+1]
    right_preOrder = preOrder[root_index+1:]

    # 递归构建左子树和右子树
    root.left = buildTree(left_inOrder, left_preOrder)
    root.right = buildTree(right_inOrder, right_preOrder)

    return root

def postOrderTraversal(root):
    if not root:
        return []

    result = []
    result.extend(postOrderTraversal(root.left))
    result.extend(postOrderTraversal(root.right))
    result.append(root.val)

    return result

# 测试代码
inOrder = [9, 3, 15, 20, 7]
preOrder = [3, 9, 20, 15, 7]
root = buildTree(inOrder, preOrder)
postOrder = postOrderTraversal(root)
print(postOrder)