用Python解决

好的，我用Python重新写一遍代码，供你参考。

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

def build_tree(inorder, postorder):
    if not inorder:
        return None
    root_val = postorder.pop()
    root = TreeNode(root_val)
    root_idx = inorder.index(root_val)
    root.right = build_tree(inorder[root_idx+1:], postorder)
    root.left = build_tree(inorder[:root_idx], postorder)
    return root

def preorder_traversal(root):
    if not root:
        return []
    res = [root.val]
    res += preorder_traversal(root.left)
    res += preorder_traversal(root.right)
    return res

inorder = [9, 3, 15, 20, 7]
postorder = [9, 15, 7, 20, 3]
root = build_tree(inorder, postorder)
print(preorder_traversal(root)) # [3, 9, 20, 15, 7]

希望这次的回答对你有所帮助！