773. 滑动谜题

在一个 2 x 3 的板上（board）有 5 块砖瓦，用数字 1~5 来表示, 以及一块空缺用 0 来表示.

一次移动定义为选择 0 与一个相邻的数字（上下左右）进行交换.

最终当板 board 的结果是 [[1,2,3],[4,5,0]] 谜板被解开。

给出一个谜板的初始状态，返回最少可以通过多少次移动解开谜板，如果不能解开谜板，则返回 -1 。

来源：力扣（LeetCode）
链接：https://leetcode-cn.com/problems/sliding-puzzle
著作权归领扣网络所有。商业转载请联系官方授权，非商业转载请注明出处。

import java.util.HashSet;
import java.util.LinkedList;
import java.util.Queue;
import java.util.Set;

class Solution {

    // 0 1 2
    // 3 4 5
    private static int[][] operations = {{1, 3}, {0, 2, 4}, {1, 5}, {0, 4}, {1, 3, 5}, {2, 4}};

    private void swap(char[] str, int a, int b) {
        char t = str[a];
        str[a] = str[b];
        str[b] = t;
    }

    private String parseString(int[][] board) {
        StringBuilder ans = new StringBuilder();
        for (int i = 0; i < board.length; ++i) {
            for (int j = 0; j < board[0].length; ++j) {
                ans.append(board[i][j]);
            }
        }
        return ans.toString();
    }

    private int getZeroIndex(int[][] board) {
        int ans = 0;
        for (int i = 0; i < board.length; ++i) {
            for (int j = 0; j < board[0].length; ++j) {
                if (board[i][j] == 0) {
                    return ans;
                }
                ans++;
            }
        }
        return ans;
    }

    public int slidingPuzzle(int[][] board) {
        if (board == null || board.length == 0 || board[0].length == 0) {
            return -1;
        }
        String start = parseString(board);
        String end = "123450";
        Set<String> visited = new HashSet<>();
        Queue<Info> queue = new LinkedList<>();
        queue.offer(new Info(start, 0, getZeroIndex(board)));
        visited.add(start);
        while (!queue.isEmpty()) {
            Info node = queue.poll();
            if (node.value.equals(end)) {
                return node.step;
            }
            String s = node.value;
            for (int x : operations[node.zeroIndex]) {
                char[] copy = s.toCharArray();
                swap(copy, node.zeroIndex, x);
                String num = new String(copy);
                if (!visited.contains(num)) {
                    queue.offer(new Info(num, node.step + 1, x));
                    visited.add(num);
                }
            }
        }
        return -1;
    }
}

class Info {
    String value;
    int step;
    int zeroIndex;

    public Info(String value, int step, int zeroIndex) {
        this.value = value;
        this.step = step;
        this.zeroIndex = zeroIndex;
    }
}