Update 二叉树相关.md

blogs/Algorithm/剑指 Offer/二叉树相关.md

@@ -595,4 +595,46 @@ class Solution {
         helper(root.left, k);
     }
 }
-```
+```
+
+#### [68 - I. 二叉搜索树的最近公共祖先](https://leetcode-cn.com/problems/er-cha-sou-suo-shu-de-zui-jin-gong-gong-zu-xian-lcof/)
+
+```java
+class Solution {
+
+    public TreeNode lowestCommonAncestor(TreeNode root, TreeNode p, TreeNode q) {
+        if (root == null) {
+            return null;
+        }
+        while (root != null) {
+            if (p.val < root.val && q.val < root.val) {
+                root = root.left;
+            } else if (p.val > root.val && q.val > root.val) {
+                root = root.right;
+            } else {
+                break;
+            }
+        }
+        return root;
+    }
+}
+```
+
+```java
+class Solution {
+
+    public TreeNode lowestCommonAncestor(TreeNode root, TreeNode p, TreeNode q) {
+        if (root == null) {
+            return null;
+        }
+        if (p.val < root.val && q.val < root.val) {
+            return lowestCommonAncestor(root.left, p, q);
+        }
+        if (p.val > root.val && q.val > root.val) {
+            return lowestCommonAncestor(root.right, p, q);
+        }
+        return root;
+    }
+}
+```
+