根据后序和中序遍历输出先序遍历python

以下是Python代码实现：

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

def preorder_traversal(root):
    if not root:
        return []
    stack, res = [root], []
    while stack:
        node = stack.pop()
        res.append(node.val)
        if node.right:
            stack.append(node.right)
        if node.left:
            stack.append(node.left)
    return res

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

输出结果为：[3, 9, 20, 15, 7]