Update 441-arranging-coins.js

Author: everthis

441-arranging-coins.js

@@ -15,3 +15,13 @@ const arrangeCoins = function(n) {
 
     return num
 };
+
+// another
+
+/**
+ * @param {number} n
+ * @return {number}
+ */
+const arrangeCoins = function(n) {
+  return (-1 + Math.sqrt(1+4*2*n)) >> 1
+};