cs: add “450. Delete Node in a BST”

Signed-off-by: Matej Focko <mfocko@redhat.com>

cs/delete-node-in-a-bst.cs

@@ -0,0 +1,45 @@
+/**
+ * Definition for a binary tree node.
+ * public class TreeNode {
+ *     public int val;
+ *     public TreeNode left;
+ *     public TreeNode right;
+ *     public TreeNode(int val=0, TreeNode left=null, TreeNode right=null) {
+ *         this.val = val;
+ *         this.left = left;
+ *         this.right = right;
+ *     }
+ * }
+ */
+public class Solution {
+    public TreeNode DeleteNode(TreeNode root, int key) {
+        if (root == null) {
+            return null;
+        }
+
+        if (key == root.val) {
+            if (root.left == null) {
+                return root.right;
+            }
+
+            if (root.right == null) {
+                return root.left;
+            }
+
+            // find successor
+            var node = root.right;
+            while (node.left != null) {
+                node = node.left;
+            }
+
+            root.val = node.val;
+            root.right = DeleteNode(root.right, node.val);
+        } else if (key < root.val) {
+            root.left = DeleteNode(root.left, key);
+        } else if (key > root.val) {
+            root.right = DeleteNode(root.right, key);
+        }
+
+        return root;
+    }
+}