/**
 *  Demo of binary search on ints.
 */
public class BinarySearch {

    // iterative binary search
    public static int binarySearchIter(int[] a, int value) {

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

        while (start <= end) {
            int middle = (start + end) / 2;
            if (value == a[middle]) {
                return middle;
            } else if (value < a[middle]) {
                end = middle - 1;
            } else {
                start = middle + 1;
            }
        }

        return -1; // not found
    }

    // recursive binary search
    public static int binarySearch(int[] a, int value) {
        return recBinarySearch(a, value, 0, a.length - 1);
    }

    // search a for value between indices start and end
    private static int recBinarySearch(int[] a, int value, int start, int end) {
        if (start > end) {
            return -1;
        } else {
            int middle = (start + end) / 2;
            if (a[middle] == value) {
                return middle;
            } else if (a[middle] < value) {
                return recBinarySearch(a, value, middle + 1, end);
            } else { // a[middle] > value
                return recBinarySearch(a, value, start, middle - 1);
            }
        }
    }

    public static void main(String[] args) {
        int[] a = {1, 3, 5, 6, 9}; // must be sorted for binary search!
        System.out.println("Found value at index " + binarySearch(a, 6));
    }

}