dfs.py

def traverse(root):
    stack, ret = [root], []
    while stack:
        cur = stack.pop()
        if isinstance(cur, Node):
            # stack.extend([cur.right, cur.left, cur.val])  # <- 前序遍历
            # stack.extend([cur.right, cur.val, cur.left])  # <- 中序遍历
            stack.extend([cur.val, cur.right, cur.left])  # <- 后序遍历
        elif isinstance(cur, int):
            ret.append(cur)
    return ret