Merge pull request #3756 from NotADucc/0069

create csharp/0069-sqrt.cs

Author: Ykhan799

csharp/0069-sqrtx.cs

@@ -0,0 +1,21 @@
+public class Solution 
+{
+    public int MySqrt(int x) 
+    {
+        int left = 0, right = x;
+        while (left <= right)
+        {
+            int mid = (left + right) >> 1;
+            long pow = (long)mid * mid;
+            if (pow <= x)
+            {
+                left = mid + 1;
+            }
+            else 
+            {
+                right = mid - 1;
+            }
+        }
+        return left - 1;
+    }
+}