OpenTheLock

class Solution {
    public int openLock(String[] deadends, String target) {
        Set<String> deadSet = new HashSet<>(Arrays.asList(deadends));
        if (deadSet.contains("0000")) return -1;
        Queue<String> queue = new LinkedList<>();
        queue.add("0000");
        int steps = 0;
        while (!queue.isEmpty()) {
            int size=queue.size();
            for (int i=0; i<size;i++) {
                String curr = queue.poll();
                if (curr.equals(target)) return steps;
                for (String nei : neighbors(curr)) {
                    if (deadSet.contains(nei)) continue;
                    deadSet.add(nei);
                    queue.offer(nei);
                }
            }
            ++steps;
        }
        return -1;
    }
    List<String> neighbors(String code) {
        List<String> result = new ArrayList<>();
        for (int i = 0; i < 4; i++) {
            int x = code.charAt(i) - '0';
            for (int diff = -1; diff <= 1; diff += 2) {
                int y = (x + diff + 10) % 10;
                result.add(code.substring(0, i) + ("" + y) + code.substring(i + 1));
            }
        }
   
        return result;
    }
}