Added a C# solution to 701. Insert into a Binary Search Tree

Author: dkiryanov

csharp/0701-insert-into-a-binary-search-tree.cs

@@ -0,0 +1,51 @@
+/**
+ * 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 InsertIntoBST(TreeNode root, int val)
+    {
+        if (root is null) return new TreeNode(val);
+
+        TreeNode cur = root;
+
+        while (cur is not null)
+        {
+            if (cur.val < val)
+            {
+                if (cur.right is null)
+                {
+                    cur.right = new TreeNode(val);
+                    break;
+                }
+
+                cur = cur.right;
+                continue;
+            }
+
+            if (cur.val > val)
+            {
+                if (cur.left is null)
+                {
+                    cur.left = new TreeNode(val);
+                    break;
+                }
+
+                cur = cur.left;
+                continue;
+            }
+        }
+
+        return root;
+    }
+}