@Override
    protected void onDeserialize(Deserializer buf) {
        super.onDeserialize(buf);
        values.clear();
        int nElements = buf.getInt(null);
        for (int i = 0; i < nElements; i++) {
            values.add(buf.getInt(null));
        }
    }
Serializes the Sketch.

Serialization format
==================
Number of elements:      4 bytes
Elements:            N * 4 bytes
@param buf Serializer
searchlib/src/main/java/com/yahoo/searchlib/aggregation/hll/SparseSketch.java