打开转盘锁

/*
 * Problem: You have a lock with four circular dials. Each dial has 10 digits: '0', '1', '2', '3', '4', '5', '6', '7', '8', '9'.
 * The dials can rotate freely: e.g., '9' can turn into '0', and '0' can turn into '9'.
 * Each move can rotate one dial by one digit.
 * The lock's initial state is '0000'.
 * A list called deadends contains numbers that cause the lock to be permanently locked if reached.
 * The string target represents the number to unlock the lock. You need to find the minimum number of moves to unlock the lock, or return -1 if it's not possible.
 */
 
import java.util.*;
import java.util.stream.*;
 
public class OpenLockStream {
    public int openLock(String[] deadends, String target) {
        Set<String> deadSet = Arrays.stream(deadends).collect(Collectors.toSet());
        if (deadSet.contains("0000")) return -1;
        if (target.equals("0000")) return 0;
 
        Set<String> visited = new HashSet<>();
        visited.add("0000");
 
        Queue<String> queue = new LinkedList<>();
        queue.offer("0000");
 
        int moves = 0;
        while (!queue.isEmpty()) {
            int size = queue.size();
            moves++;
            for (int i = 0; i < size; i++) {
                String current = queue.poll();
                List<String> nextStates = IntStream.range(0, 4)
                    .mapToObj(j -> Stream.of(-1, 1)
                        .map(d -> rotate(current, j, d))
                        .collect(Collectors.toList()))
                    .flatMap(Collection::stream)
                    .collect(Collectors.toList());
                for (String next : nextStates) {
                    if (next.equals(target)) return moves;
                    if (!visited.contains(next) && !deadSet.contains(next)) {
                        queue.offer(next);
                        visited.add(next);
                    }
                }
            }
        }
        return -1;
    }
 
    private String rotate(String state, int index, int direction) {
        char[] chars = state.toCharArray();
        chars[index] = (char)((chars[index] - '0' + direction + 10) % 10 + '0');
        return new String(chars);
    }
}