ltail.left = None
ltail.right = None
return root, ltail
elif root.left is not None and root.right is not None:
lhead, ltail = gao(root.left)
rhead, rtail = gao(root.right)
root.left = None
root.right = lhead
lhead.left = None
ltail.left = None
ltail.right = rhead
rhead.left = None
rtail.left = None
rtail.right = None
return root, rtail
gao(root)
solver = Solution()
root5 = TreeNode()
root5.build_from_list([1,2,3,4])
solver.flatten(root5)
print(root5.to_dict())
root4 = TreeNode()
root4.build_from_list([2,1,4,None,None,3,5])
solver.flatten(root4)
print(root4.to_dict())
