queue.offer(combination);
    visited.add(formatConvination(combination));
    int levels = process(queue, Arrays.asList(deadends), visited, target, 0);

    return levels;
}

private int process(Queue<int[]> queue, List deadends, Set<String> visited, String target, int level) {
    Queue<int[]> nextLevel = new LinkedList<>();

    for (int[] node : queue) {
        String nodeStr = formatConvination(node);
        if (deadends.contains(nodeStr)) {
            continue;
        }

        if (nodeStr.compareTo(target) == 0) {
            return level;
        }

        for (int j = 0; j < target.length(); j++) {
            int[] up = makeMovementUp(node, j);
            String upStr = formatConvination(up);
            if (!deadends.contains(upStr) && !visited.contains(upStr)) {
                nextLevel.offer(up);
                visited.add(upStr);
            }
            int[] down = makeMovementDown(node, j);
            String downStr = formatConvination(down);
            if (!deadends.contains(downStr) && !visited.contains(downStr)) {
                nextLevel.offer(down);
                visited.add(downStr);
            }
        }
    }

    if (!nextLevel.isEmpty()) {
        return process(nextLevel, deadends, visited, target, ++level);
    } else {
        return -1;
    }
}

private String formatConvination(int[] combination) {
    return String.format("%d%d%d%d", combination[0], combination[1], combination[2], combination[3]);
}

private int[] makeMovementUp(int[] combination, int position) {
    int[] newCombination = Arrays.copyOf(combination, combination.length);
    newCombination[position] = newCombination[position] == 9 ? 0 : newCombination[position] +1;
    return newCombination;
}

private int[] makeMovementDown(int[] combination, int position) {
    int[] newCombination = Arrays.copyOf(combination, combination.length);
    newCombination[position] = newCombination[position] == 0 ? 9 : newCombination[position] -1;
    return newCombination;
}