必须要确保，如果做右旋，顶端节点必须有一个左子节点。

You must be sure that, if you're doing a right rotation, the top node has a left child.

youdao

换句话说，就是一个有右子节点的节点的可能接左子节点的位置，或者是有左子节点的节点的可能接右子节点位置。

In other words, it's the potential left child of a node with a right child, or the potential right child of a node with a left child. This will make more sense as we go along.

youdao

而子节点也是这样一个节点，也有一个左节点和一个右节点，当然也可以没有子节点，也就是说一个节点可能有零个或者两个子节点。

Each child is itself a node, and either or both of the child nodes can be null, meaning that a node may have zero to two children.

youdao

而子节点也是这样一个节点，也有一个左节点和一个右节点，当然也可以没有子节点，也就是说一个节点可能有零个或者两个子节点。

Each child is itself a node, and either or both of the child nodes can be null, meaning that a node may have zero to two children.

youdao