int binarySearch(int[] array, int key) {
    int left = 0, right = array.length - 1;
    while (left <= right) {
        int mid = left + (right - left) / 2;
        if (array[mid] == key)
            return mid;
        if (array[mid] < key)
            left = mid + 1;
        else
            right = mid - 1;
    }
    return -1;
}