public static void main(final String[] args) {
        // "CAA","AAA","BCD"], "AAB
        final char[][] board = new char[][] { { 'c', 'a', 'a' },
                { 'a', 'a', 'a' },
                { 'b', 'c', 'd' } };
        final String word = "aab";
        final WordSearch ws = new WordSearch();
        if (ws.exist(board, word)) {
            System.out.println("passed");
        } else {
            System.out.println("failed");
        }
    }