Update 二叉树相关.md

blogs/Algorithm/剑指 Offer/二叉树相关.md

@@ -638,3 +638,19 @@ class Solution {
 }
 ```
 
+#### [68 - II. 二叉树的最近公共祖先](https://leetcode-cn.com/problems/er-cha-shu-de-zui-jin-gong-gong-zu-xian-lcof/)
+
+```java
+class Solution {
+    public TreeNode lowestCommonAncestor(TreeNode root, TreeNode p, TreeNode q) {
+        if(root == null || root == p || root == q) return root;
+        TreeNode left = lowestCommonAncestor(root.left, p, q);
+        TreeNode right = lowestCommonAncestor(root.right, p, q);
+        if(left == null && right == null) return null; // 1.
+        if(left == null) return right; // 3.
+        if(right == null) return left; // 4.
+        return root; // 2. if(left != null and right != null)
+    }
+}
+```
+