36. Valid Sudoku

 1  public boolean isValidSudoku(char[][] board) {
 2         if(board == null || board.length == 0) {
 3             return false;
 4         }
 5         for(int i = 0; i < 9; i += 3) {
 6             for(int j = 0; j < 9; j += 3) {
 7                 boolean temp = checkSquare(board, i, j);
 8                 if(temp == false) {
 9                     return false;
10                 }
11             }
12         }
13         for(int i = 0; i < 9; i++) {
14             boolean temp = checkCol(board, i);
15             if(temp == false) {
16                 return false;
17             }
18             temp = checkRow(board, i);
19             if(temp == false) {
20                 return false;
21             }
22         }
23         return true;
24     }
25     
26     private boolean checkCol(char[][] board, int col) {
27         HashSet<Character> set = new HashSet<Character>();
28         for(int i = 0; i < 9; i++) {
29             char x = board[i][col];
30             if(x != ‘.‘) {
31                 if(set.contains(x)) {
32                     return false;
33                 } else {
34                     set.add(x);
35                 }
36             }
37         }
38         return true;
39     }
40     
41     private boolean checkRow(char[][] board, int row) {
42         HashSet<Character> set = new HashSet<Character>();
43         for(int i = 0; i < 9; i++) {
44             char x = board[row][i];
45             if(x != ‘.‘) {
46                 if(set.contains(x)) {
47                     return false;
48                 } else {
49                     set.add(x);
50                 }
51             }
52         }
53         return true;
54     }
55     
56     private boolean checkSquare(char[][] board, int row, int col) {
57         HashSet<Character> set = new HashSet<Character>();
58         for(int i = row; i < row + 3; i++) {
59             for(int j = col; j < col + 3; j++) {
60                 char x = board[i][j];
61                 if(x != ‘.‘) {
62                     if(set.contains(x)) {
63                         return false;
64                     } else {
65                         set.add(x);
66                     }
67                 }
68             }
69         }
70         return true;
71     }