13.3 Binary Search

public class BinarySearch {
    // Returns index of x if it is present in arr[l..
    // r], else return -1
    public static int binarySearch(int arr[], int l, int r, int x) {
        if (r >= l) {
            int mid = l + (r - l) / 2;

            // If the element is present at the
            // middle itself
            if (arr[mid] == x) return mid;

            // If element is smaller than mid, then
            // it can only be present in left subarray
            if (arr[mid] > x) return binarySearch(arr, l, mid - 1, x);

            // Else the element can only be present
            // in right subarray
            return binarySearch(arr, mid + 1, r, x);
        }

        // We reach here when element is not present
        // in array
        return -1;
    }