class SparseVector extends Vector {

    @Override
    public double normL2Square() {
        double d = 0;
        for (double t : values) {
            d += t * t;
        }
        return d;
    }

    public  SparseVector();
    public  SparseVector(int n);
    public  SparseVector(int n, int[] indices, double[] values);
    public  SparseVector(int n, Map<Integer, Double> kv);

}