RBS.java

// Leetcode Question - https://leetcode.com/problems/search-in-rotated-sorted-array/
// Rotated Binary Search 


public class RBS
{
    public static void main(String[] args)
    {
        int[] arr = {4,5,6,7,0,1,2};
        int target = 0;
        int ans = search(arr,target);
        System.out.println(ans);

    }

    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 - start) / 2; // might be possible that start + end may exceed the range of integers in java 
            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] <= start)
            {
               end = mid - 1;
            }
            else
            {
               start = mid + 1;
            }
        }
        return -1;
    }
}