@Override
    public long estimateCount(Sketch<?> sketch) {
        if (sketch instanceof NormalSketch) {
            return estimateCount((NormalSketch) sketch);
        } else {
            return estimateCount((SparseSketch) sketch);
        }
    }
Estimates the number of unique elements.

@param sketch A sketch populated with values from the aggregation phase of HLL.
@return The estimated number of unique elements.
searchlib/src/main/java/com/yahoo/searchlib/aggregation/hll/HyperLogLogEstimator.java