IE Intersect from Union cardinality

iei.java

    public long getIntersection(List<HLL> hllList) {
        for(HLL hll:hllList) {
            logger.debug("Individual cardinality of " + hll.cardinality());
        }
        logger.debug("get intersection of hllList = " + hllList);
        if(hllList.size() == 1) {
            HLL hllObject = hllList.get(0);
            logger.debug("Single Cardinality " + hllObject.toString() + " = " + hllObject.cardinality());
            return hllObject.cardinality();
        }

        long totalUnion = HLLUtil.unionHLL(hllList).cardinality();
        logger.debug("Total Union is " + totalUnion);
        long totalSubSum = 0;
        for(int k = 1; k < hllList.size(); k++) {
            long setTotalSubSum = 0;
            List<List<HLL>> hllCombinations = HLLUtil.generateCombination(k, hllList);
            logger.debug("HLL Combinations at k = " + k + " is " + hllCombinations.size());
            for(List<HLL> hllCombination: hllCombinations) {
                setTotalSubSum += getIntersection(hllCombination);
            }
            totalSubSum += (long) (Math.pow(-1, k+1)*setTotalSubSum);
            logger.debug("Total sub sum at k = " + k + ", subsum = " + setTotalSubSum);
        }
        logger.debug("Total sum of subset intersections = " + totalSubSum);

        long totalCardinality = (long) ((totalUnion - totalSubSum)/Math.pow(-1, hllList.size() + 1));
        logger.debug("Cardinality is " + totalCardinality);
        return totalCardinality;
    }