LeetCode: Valid Sudoku 解题报告

Valid Sudoku
Determine if a Sudoku is valid, according to: Sudoku Puzzles - The Rules.

The Sudoku board could be partially filled, where empty cells are filled with the character '.'.

A partially filled sudoku which is valid.

Note:
A valid Sudoku board (partially filled) is not necessarily solvable. Only the filled cells need to be validated.

 

SOLUTION:

使用HashSet 行列，9块分别检查。

 1 public class Solution {
 2     public boolean isValidSudoku(char[][] board) {
 3         if (board == null || board.length != 9 ||
 4             board[0].length != 9) {
 5             return false;
 6         }
 7         
 8         HashSet<Character> set = new HashSet<Character>();
 9         
10         // check the rows.
11         for (int i = 0; i < 9; i++) {
12             // clear the set at every row.
13             set.clear();
14             for (int j = 0; j < 9; j++) {
15                 if (!isValidChar(board[i][j], set)) {
16                     return false;
17                 }
18             }
19         }
20         
21         // check the columns.
22         for (int i = 0; i < 9; i++) {
23             // clear the set at every column.
24             set.clear();
25             for (int j = 0; j < 9; j++) {
26                 if (!isValidChar(board[j][i], set)) {
27                     return false;
28                 }
29             }
30         }
31         
32         // check the blocks.
33         for (int i = 0; i < 9; i+=3) {
34             for (int j = 0; j < 9; j+=3) {
35                 // clear the set at every block.
36                 set.clear();
37                 for (int k = 0; k < 9; k++) {
38                     if (!isValidChar(board[i + k / 3][j + k % 3], set)) {
39                         return false;
40                     }    
41                 }
42             }
43         }
44         
45         return true;
46     }
47     
48     public boolean isValidChar(char c, HashSet<Character> set) {
49         if (c == '.') {
50             return true;
51         }
52         
53         if (c < '0' || c > '9') {
54             return false;
55         }
56         
57         // Check if the character exit in the hashset.
58         if (set.contains(c)) {
59             return false;
60         }
61         
62         set.add(c);
63         
64         return true;
65     }
66 }
View Code

2013.1.13 redo:

 1 public class Solution {
 2     public boolean isValidSudoku(char[][] board) {
 3         // 2:03
 4         if (board == null || board.length == 0 || board[0].length == 0) {
 5             return false;
 6         }
 7         
 8         int rows = board.length;
 9         int cols = board[0].length;
10         
11         // exam the rows.
12         for (int i = 0; i < rows; i++) {
13             HashSet<Character> set = new HashSet<Character>();
14             for (int j = 0; j < cols; j++) {
15                 char c = board[i][j];
16                 if (c != '.') {
17                     if (set.contains(c)) {
18                         return false;
19                     }
20                     set.add(c);
21                 }
22             }
23         }
24         
25         // exam the cols.
26         for (int i = 0; i < cols; i++) {
27             HashSet<Character> set = new HashSet<Character>();
28             for (int j = 0; j < rows; j++) {
29                 // bug 1: should use board[j][i]
30                 char c = board[j][i];
31                 if (c != '.') {
32                     if (set.contains(c)) {
33                         return false;
34                     }
35                     set.add(c);
36                 }
37             }
38         }
39         
40         // examp the square.
41         for (int i = 0; i < rows; i += 3) {
42             for (int j = 0; j < cols; j += 3) {
43                 HashSet<Character> set = new HashSet<Character>();
44                 for (int k = 0; k < 9; k++) {
45                     char c = board[i + k / 3][j + k % 3];
46                     if (c == '.') {
47                         continue;
48                     }
49                     
50                     if (set.contains(c)) {
51                         return false;
52                     }
53                     set.add(c);
54                 }
55             }
56         }
57         
58         return true;
59     }
60 }
View Code

 

主页君的GITHUB:

https://github.com/yuzhangcmu/LeetCode_algorithm/blob/master/hash/IsValidSudoku.java

 

ref: http://www.ninechapter.com/solutions/valid-sudoku/

posted on 2014-11-01 19:15  Yu's Garden  阅读(1898)  评论(0)  编辑  收藏  举报

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