1 public static boolean exist(char[][] board, String word) {
 2         if (board == null) return false;
 3         if (word.length() == 0) return true;
 4         int row = board.length;
 5         if (row == 0) return false;
 6         int col = board[0].length;
 7         if (col == 0) return false;
 8         boolean visited[][] = new boolean[board.length][board[0].length];
 9         for (int i=0; i<row; i++) {
10             for (int j=0; j<col; j++) {
11 //                boolean visited[][] = new boolean[board.length][board[0].length];
12                 if (dfs(board, i, j, word, 0, visited))
13                     return true;
14             }
15         }
16         return false;
17     }
18
19     public static boolean dfs(char[][] board, int i, int j, String word, int position, boolean visited[][]) {
20         if (i<0 || i>=board.length || j<0 || j>=board[0].length) return false;
21         if (visited[i][j] || board[i][j] != word.charAt(position)) return false;
22         if (position == word.length()-1) return true;
23
24         visited[i][j] = true;
25         boolean result = dfs(board, i-1, j, word, position+1, visited) ||
26                          dfs(board, i, j+1, word, position+1, visited) ||
27                          dfs(board, i+1, j, word, position+1, visited) ||
28                          dfs(board, i, j-1, word, position+1, visited);
29         visited[i][j] = false;
30         return result;
31     }