non-naive-adv-2020-3-elem.txt

	private static long nonNaive(List<Long> values, long sum) {
		Long result = null;
		List<Long> sorted = values.stream().filter(x -> x <= (SUM - 2)).collect(Collectors.toList());
		sorted.sort(Comparator.naturalOrder());
		for (int i = 0; result == null && i < sorted.size() - 2; ++i) {
			long a = sorted.get(i);
			boolean offRange = false;
			for (int j = i; !offRange && result == null && j < sorted.size() - 1; ++j) {
				long b = sorted.get(j);
				long partial = a + b;
				offRange = partial >= (SUM - b);
				if (!offRange) {
					// search third addendum
					long toBeFound = SUM - partial;
					int k = j + i + Collections.binarySearch(sorted.subList(j + 1, sorted.size()), toBeFound);
					if (k > j) {
						// found match that sums to 2020
						// now calculating the result
						result = a * b * toBeFound;
					}
				}
			}
		}
		return result;
	}