RotatedBinarySearch.java

package com.company;
// https://leetcode.com/problems/search-in-rotated-sorted-array/
public class RotatedBS {
    public static void main(String[] args) {
        int[] arr = {4,5,6,7,0,1,2};
        System.out.println(findPivot(arr));
    }

    static int search(int[] nums, int target){
        int pivot = findPivot(nums);

        // if you did not find a pivot, it means the array is not rotated
        if(pivot == -1){
            // just do normal binary search
            return binarySearch(nums, target, 0, nums.length - 1);
        }
        // if pivot is found, you have found 2 asc sorted arrays
        if(nums[pivot] == target){
            return pivot;
        }

        if(target >= nums[0]){
            return binarySearch(nums, target, 0, pivot - 1);
        }

        return binarySearch(nums, target, pivot + 1, nums.length - 1);
    }

    static int binarySearch(int[] arr, int target, int start, int end){

        while(start <= end){
            // find the middle element
//           int mid = (start + end) / 2; // might be possible that (start+end) exceeds the range of int in Java
            int mid = start + (end - start) / 2; // same as above but better way

            if(target < arr[mid]){
                end = mid - 1;
            } else if(target > arr[mid]){
                start = mid + 1;
            } else {
                // ans found
                return mid;
            }
        }
        return -1;
    }

    static int findPivot(int[] arr){
        int start = 0;
        int end = arr.length - 1;
        while(start <= end){
            int mid = start + (end - start) / 2;
            // 4 cases over here
            if(mid < end && arr[mid] > arr[mid + 1]){
                return mid;
            }
            if(mid > start && arr[mid] < arr[mid - 1]){
                return mid - 1;
            }
            if(arr[mid] <= arr[start]){
                end = mid - 1;
            } else{
                start = mid + 1;
            }
        }
        return -1;
    }

    static int findPivotwithDuplicates(int[] arr){
        int start = 0;
        int end = arr.length - 1;
        while(start <= end){
            int mid = start + (end - start) / 2;
            // 4 cases over here
            if(mid < end && arr[mid] > arr[mid + 1]){
                return mid;
            }
            if(mid > start && arr[mid] < arr[mid - 1]) {
                return mid - 1;
            }

            // if elements at middle, start, end  are equal then just skip the duplicates
            if(arr[mid] == arr[start] && arr[mid] == arr[end]){
                // skip the duplicates
                // NOTE: what if these elements at start and end were the pivot??
                // check if start is pivot
                if(arr[start] > arr[start + 1]){
                    return start;
                }
                start++;

                // check whether end is pivot
                if(arr[end] < arr[end - 1]){
                    return end - 1;
                }
                end--;
            }
            // left side is sorted, so pivot should be in right
            else if(arr[start] < arr[mid] || (arr[start] == arr[mid] && arr[mid] > arr[mid])){
                start = mid + 1;
            }
            else{
                end = mid - 1;
            }
        }
        return -1;
    }
}