OrderAgnosticBS.java

package com.viraj;

public class OrderAgnosticBS {
    public static void main(String[] args) {
        int[] arr = {-18, -12, -4, 0, 2, 3, 4, 15, 16, 18, 22, 45, 89};
        int target = 5;
        int ans = orderAgnosticBS(arr,target);
        System.out.println(ans);
    }

    static int orderAgnosticBS(int[] arr, int target){

        int start = 0;
        int end = arr.length - 1;

        //find whether the array is sorted in ascending or descending.
        boolean isAsc = arr[start] < arr[end];



        while(start <= end){
            //find the middle element
            //int mid = (start + end) / 2; //might be possible that (start + end ) exceeds the range of int.
            int mid = start + (end-start)/2;

            if(arr[mid] == target) return mid;

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