Java 九宫重排(满分解法)

(pos%3 != index%3 && pos/3 != index/3)

import java.util.*;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        String start = sc.next();
        String end = sc.next();

		// 枚举字符串下标的上下左右
        int[] upDownLeftRight = {-3,3,-1,1};
        // 去重
        Set<String> set = new HashSet<>();
        Queue<String> queue = new LinkedList<>();
        set.add(start);
        queue.offer(start);

        int count = 0;
        // 标记是否已经找到
        boolean flag = false;
        while (!queue.isEmpty()) {
            int size = queue.size();
            while (size-- != 0) {
                String s =  queue.peek();
                // 空格位置
                int index = s.indexOf(".");
                for (int i = 0; i < 4; i++) {
                    int pos = index + upDownLeftRight[i];
                    // 当新的位置不是空格的上下左右或者已经越界
                    if (pos < 0 || pos > 8 || (pos%3 != index%3 && pos/3 != index/3)) {
                        continue;
                    }

                    char c = s.charAt(pos);
                    char[] ch = s.toCharArray();
                    ch[pos] = ch[index];
                    ch[index] = c;

                    String str = new String(ch);
                    if (str.equals(end)) {
                        flag = true;
                        break;
                    }
                    if (set.add(str)) {
                        queue.offer(str);
                    }

                }
                queue.poll();
            }
            count++;
            if (flag) {
                break;
            }
        }
        if (flag) {
            System.out.println(count);
        } else {
            System.out.println(-1);
        }
    }
}