Valid Sudoku

 1 class Solution {
 2     /**
 3       * @param board: the board
 4         @return: wether the Sudoku is valid
 5       */
 6     public boolean isValidSudoku(char[][] board) {
 7         boolean[] visited = new boolean[9];
 8         
 9         // row
10         for(int i = 0; i < 9; i++){
11             Arrays.fill(visited, false);
12             for(int j = 0; j < 9; j++){
13                 if(!process(visited, board[i][j]))
14                     return false;
15             }
16         }
17         
18         //col
19         for(int i = 0; i < 9; i++){
20             Arrays.fill(visited, false);
21             for(int j = 0; j < 9; j++){
22                 if(!process(visited, board[j][i]))
23                     return false;
24             }
25         }
26         
27         // sub matrix
28         for(int i = 0; i < 9; i += 3){
29             for(int j = 0; j < 9; j += 3){
30                 Arrays.fill(visited, false);
31                 for(int k = 0; k < 9; k++){
32                     if(!process(visited, board[i + k / 3][ j + k % 3]))
33                     return false;                   
34                 }
35             }
36         }
37         return true;
38     }
39     
40     private boolean process(boolean[] visited, char digit){
41         if(digit == ‘.‘){
42             return true;
43         }
44         
45         int num = digit - ‘0‘;
46         if ( num < 1 || num > 9 || visited[num-1]){
47             return false;
48         }
49         
50         visited[num - 1] = true;
51         return true;
52     }
53 };