Backtracking_79. 单词搜索

board =
[
[‘A‘,‘B‘,‘C‘,‘E‘],
[‘S‘,‘F‘,‘C‘,‘S‘],
[‘A‘,‘D‘,‘E‘,‘E‘]
]

给定 word = "ABCCED", 返回 true
给定 word = "SEE", 返回 true
给定 word = "ABCB", 返回 false 

class Solution {
    //定义一个方向标
    static final int[][] DIRS = new int[][]{{-1,0}, {1,0}, {0,-1},{0,1}};
    static int row , col;
    public static boolean exist(char[][] board, String word){
        //特殊情况判断
        if (board == null || board.length == 0 || board[0].length == 0){
            return false;
        }
        if (word.length() == 0){
            return true;
        }
        row = board.length;
        col = board[0].length;
        boolean [][] isVisited = new boolean[row][col];
        for (int i = 0; i < row; i++) {
            for (int j = 0; j < col; j++) {
                if (dfs(0,i,j,board,isVisited,word)){
                    return true;
                }
            }
        }
        return false;
    }

    public static boolean dfs(int curLen, int i ,int j, char [][] board, boolean [][] isVisited,String word){
        if (curLen == word.length()) {
            return true;
        }
        //排除所有的不符合的条件
        if (i < 0 || i >= row || j < 0 || j >= col || board[i][j] != word.charAt(curLen) || isVisited[i][j]) {
            return false;
        }
        //进来了就说明这个点已经访问过了
        isVisited[i][j] = true;
        for (int[] d : DIRS) {
            if (dfs(curLen + 1, i + d[0], j + d[1], board, isVisited, word)) {
                return true;
            }
        }
        isVisited[i][j] = false;
        return false;
    }
}