better implementation after reading answer

Author: amejiarosario

rotate-string.js

@@ -1,4 +1,32 @@
+// O (n)
 function isStringRotation(s1, s2) {
+  return isSubstring(s1 + s1, s2);
+}
+
+function isSubstring(s1, s2) {
+  return s1.indexOf(s2) > -1 || s2.indexOf(s1) > -1;
+}
+
+console.log(isStringRotation('ab', 'ab'));
+console.log(isStringRotation('ba', 'ab'));
+
+console.log(isStringRotation('aab', 'aab'));
+console.log(isStringRotation('aba', 'aab'));
+console.log(isStringRotation('baa', 'aab'));
+
+
+console.log(isStringRotation('aaaab', 'aaaab'));
+console.log(isStringRotation('aaaba', 'aaaab'));
+console.log(isStringRotation('aabaa', 'aaaab'));
+console.log(isStringRotation('abaaa', 'aaaab'));
+console.log(isStringRotation('baaaa', 'aaaab'));
+
+console.log(isStringRotation('waterbottle', 'bottlewater'));
+
+console.log(isStringRotation('waterbotlle', 'bottlewater')); // false
+
+// O (n^2)
+function isStringRotationSlow(s1, s2) {
   if(s1.length !== s2.length) {
     return false;
   }
@@ -21,24 +49,4 @@ function isStringRotation(s1, s2) {
     }
   }
   return false;
-}
-
-function isSubstring(s1, s2) {
-  return s1.indexOf(s2) > -1 || s2.indexOf(s1) > -1;
-}
-
-console.log(isStringRotation('ab', 'ab'));
-console.log(isStringRotation('ba', 'ab'));
-
-console.log(isStringRotation('aab', 'aab'));
-console.log(isStringRotation('aba', 'aab'));
-console.log(isStringRotation('baa', 'aab'));
-
-
-console.log(isStringRotation('aaaab', 'aaaab'));
-console.log(isStringRotation('aaaba', 'aaaab'));
-console.log(isStringRotation('aabaa', 'aaaab'));
-console.log(isStringRotation('abaaa', 'aaaab'));
-console.log(isStringRotation('baaaa', 'aaaab'));
-
-console.log(isStringRotation('waterbottle', 'bottlewater'));
+}