Merge pull request #866 from pontusdacke/136-Single-Number

Add csharp solution for 136 Single Number

Author: Ahmad-A0

csharp/136-Single-Number.cs

@@ -0,0 +1,10 @@
+public class Solution {
+    public int SingleNumber(int[] nums) {
+        var x = 0;
+        for (int i=0;i < nums.Length; i++)
+        {
+            x ^= nums[i];
+        }
+        return x;
+    }
+}