矩阵中的路径12

给定一个 m x n 二维字符网格 board 和一个字符串单词 word 。如果 word 存在于网格中，返回 true ；否则，返回 false 。

• 字符串转换为数组：char[] words = word.toCharArray(); char[] word
• board[i][j] = ‘’;

class Solution {
    public boolean exist(char[][] board, String word) {
        char[] words = word.toCharArray();
        for(int i = 0; i < board.length; i++) {
            for(int j = 0; j < board[0].length; j++) {
                if(dfs(board, words, i, j, 0)) return true;
            }
        }
        return false;
    }
     //找单独一个i，j位置的
    boolean dfs(char[][] board, char[] word, int i, int j, int k) {
        if(i >= board.length || i < 0 || j >= board[0].length || j < 0 || board[i][j] != word[k]) return false;
        //对于传入的参数i，j以及board[i][j]==words[k]进行判断
        if(k == word.length - 1) return true;
        board[i][j] = '';//通过上一个筛选 ij满足 且board[i][j] == word[k]
        boolean res = dfs(board, word, i + 1, j, k + 1) || dfs(board, word, i - 1, j, k + 1) || 
                      dfs(board, word, i, j + 1, k + 1) || dfs(board, word, i , j - 1, k + 1);
        board[i][j] = word[k];//恢复board的值
        return res;
    }
}