Implrove find rotated index solution to O(log n)

Author: KarenOk

Divide and Conquer/findRotatedIndex.js

@@ -17,12 +17,7 @@
 
 function findRotatedIndex(arr, num) {
 let index;
-let pivot;
-
-// find pivot
-for (let i = 0; i < arr.length - 1; i++) {
-if (arr[i] > arr[i + 1]) pivot = i;
-}
+let pivot = findPivot(arr, 0, arr.length - 1); // find pivot
 
 function helper(start, end) {
 if (index) return;
@@ -41,3 +36,16 @@ function findRotatedIndex(arr, num) {
 
 return index ? index : -1;
 }
+
+function findPivot(arr, start, end) {
+if (start > end) return -1;
+else if (start === end) return start;
+
+let mid = Math.floor((start + end) / 2);
+
+if (arr[mid] > arr[end]) {
+return findPivot(arr, mid + 1, end);
+} else {
+return findPivot(arr, start, mid);
+}
+}