add solution

Author: Neil94n

solution/0069.Sqrt(x)/Solution.js

@@ -0,0 +1,18 @@
+/**
+ * @param {number} x
+ * @return {number}
+ */
+var mySqrt = function(x) {
+    var left = 1
+    var right = x    
+    var middle = Math.floor((left + right) / 2)    
+    while( middle !== left ) {
+        if (middle * middle <= x) {
+            left = middle
+        } else {
+            right = middle
+        }
+        middle = Math.floor((left + right) / 2)
+    }    
+    return middle
+};