binary search

public static int search(int[] elements, int key) {
    int low = 0;
    int high = elements.length - 1;

    while (low <= high) {
        int mid = low + (high - low) / 2;
        if (key < elements[mid]) {
            high = mid - 1;
        } else if (key > elements[mid]) {
            low = mid + 1;
        } else {
            return mid;
        }
    }
    return -1;
}