[leetcode] Word Search

public class Solution {
    public boolean exist(char[][] board, String word) {
        if (word == null || board == null || word.equals(""))
            return false;

        int m = board.length;
        int n = board[0].length;
        boolean visit[][] = new boolean[m][n];

        for (int i = 0; i < m; i++)
            for (int j = 0; j < n; j++) {
                boolean res = dfs(board, visit, i, j, word, 0);
                if (res)
                    return true;
            }

        return false;

    }

    private int offset[][] = new int[][] { { 1, 0 }, { -1, 0 }, { 0, -1 }, { 0, 1 } };

    private boolean dfs(char[][] board, boolean[][] visit, int x, int y, String word, int cur) {
        // System.out.println("dfs:"+x+","+y+","+cur);

        if (board[x][y] != word.charAt(cur))
            return false;

        if (cur == word.length() - 1) {
            return true;
        }

        int m = board.length;
        int n = board[0].length;

        visit[x][y] = true;
        int nx, ny;
        for (int i = 0; i < 4; i++) {
            nx = x + offset[i][0];
            ny = y + offset[i][1];

            if (nx >= 0 && nx < m && ny >= 0 && ny < n && !visit[nx][ny]) {
                boolean res = dfs(board, visit, nx, ny, word, cur + 1);
                if (res)
                    return true;
            }

        }
        visit[x][y] = false;

        return false;

    }

    public static void main(String[] args) {
        char[][] board;
        String word;
        board = new char[][] { { ‘A‘, ‘B‘, ‘C‘, ‘E‘ }, { ‘S‘, ‘F‘, ‘C‘, ‘S‘ }, { ‘A‘, ‘D‘, ‘E‘, ‘E‘ } };
        word = "ASA";
        System.out.println(new Solution().exist(board, word));

        board = new char[][] { { ‘b‘ } };
        word = "b";
        System.out.println(new Solution().exist(board, word));

    }

}