public static int[] numberOf(String s) {
        int[] a= new int[4];
        for (int k= 0; k < s.length(); k= k+1) {
            switch (s.charAt(k)) {
                case 'C': a[0]= a[0] + 1; break;
                case 'A': a[1]= a[1] + 1; break;
                case 'T': a[2]= a[2] + 1; break;
                case 'G': a[3]= a[3] + 1; break;
                default:
            }
        }
        return a;
    }