Open the Lock

import java.util.*;

class Solution {
    public int openLock(String[] deadends, String target) {
        Set<String> seen = new HashSet<>(Arrays.asList(deadends));
        if (seen.contains("0000")) return -1;
        Deque<String> q = new ArrayDeque<>();
        q.offer("0000");
        seen.add("0000");
        for (int steps = 0; !q.isEmpty(); steps++) {
            for (int size = q.size(); size > 0; size--) {
                String s = q.poll();
                if (s.equals(target)) return steps;
                char[] c = s.toCharArray();
                for (int i = 0; i < 4; i++) {
                    char orig = c[i];
                    for (int d : new int[]{1, 9}) {
                        c[i] = (char) ('0' + (orig - '0' + d) % 10);
                        String t = new String(c);
                        if (seen.add(t)) q.offer(t);
                    }
                    c[i] = orig;
                }
            }
        }
        return -1;
    }
}