InfiniteArray.java

/* Given an infinite sorted array. Find position of element in this array */


//since it is an infinite array therefore arr.length cannot be used to find end. But we need to find end for binary search. So we take chunks/small sizes of boxes for finding start end range

public class InfiniteArray {
    public static void main(String[] args) {
        int[] arr = {3, 5, 7, 9, 10, 90,
                100, 130, 140, 160, 170};
        int target = 10;
        System.out.println(ans(arr, target));
    }
    static int ans(int[] arr, int target) {
        // first find the range
        // first start with a box of size 2
        int start = 0;
        int end = 1;

        // condition for the target to lie in the range
        while (target > arr[end]) {
            int temp = end + 1; // this is my new start
          
            // double the box value
            // end = previous end + sizeofbox*2
            end = end + (end - start + 1) * 2;
            start = temp;
        }
        return binarySearch(arr, target, start, end);

    }
    static int binarySearch(int[] arr, int target, int start, int end) {
        while(start <= end) {
            int mid = start + (end - start) / 2;

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