public class Main {
    public static void main(String[] args) {
        int [] arr= {1,2,3,4,5,6,7,8,9,10};
        int target = 5; // which element are we looking for
        int ans = binarySearch(arr,target);
        System.out.println(ans);

    }

    static int binarySearch(int[] arr,int target) {
        int start = 0;
        int end = arr.length - 1;

        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;// ans found
            }
        }
        return -1; // item does not exist in the array
    }
}