找了下答案，分享给评论区的 xdm
```java
/*
// Definition for a Node.
class Node {
public int val;
public Node left;
public Node right;
public Node parent;
};
*/
class Solution {
public Node lowestCommonAncestor(Node p, Node q) {
Node a = p, b = q;
while (a != b) {
a = a.parent == null ? q : a.parent;
b = b.parent == null ? p : b.parent;
}
return a;
}
}
```
