add code of 235

Author: Li Li

top-interview-questions/235. Lowest Common Ancestor of a Binary Search Tree.cs

@@ -1,3 +1,4 @@
+// general one for BT not only BST
 public class Solution {
     public TreeNode LowestCommonAncestor(TreeNode root, TreeNode p, TreeNode q) {
         if (root == null) return null;
@@ -8,4 +9,17 @@ public TreeNode LowestCommonAncestor(TreeNode root, TreeNode p, TreeNode q) {
         else if (left == null) return right;
         else return left;
     }
+}
+
+// specific for BST
+public class Solution {
+    public TreeNode LowestCommonAncestor(TreeNode root, TreeNode p, TreeNode q) {
+        if (root.val > p.val && root.val > q.val) {
+            return LowestCommonAncestor(root.left, p, q);
+        } else if (root.val < p.val && root.val < q.val) {
+            return LowestCommonAncestor(root.right, p, q);
+        } else {
+            return root;
+        }
+    }
 }