@NotNull
  private static Couple<Integer> hashChildResults(TreeHashResult[] childResults, int multiplier) {
    int[] hashes = getHashes(childResults);
    int[] costs = getCosts(childResults);

    int hash = AbstractTreeHasher.vector(hashes, multiplier);
    int cost = AbstractTreeHasher.vector(costs);

    return Couple.of(hash, cost);
  }
@NotNull
  private static Couple<Integer> hashChildResults(TreeHashResult[] childResults, int multiplier)