[leetcode]Valid Sudoku

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.

算法思路：

逐行逐列判断行列是否有冲突，然后再逐块判断。

从网上看到有位大拿写的矩阵标记法，第二遍看继续亮瞎。不敢班门弄斧，然后上人家的算法吧。

代码如下：

 1 public class Solution {
 2     public boolean isValidSudoku(char[][] board) {
 3         if(board == null || board.length != 9 || board[0].length != 9) return false;
 4         boolean[][] row = new boolean[9][9];
 5         boolean[][] col = new boolean[9][9];
 6         boolean[][] matrix = new boolean[9][9];
 7         for(int i = 0; i < 9; i++){
 8             for(int j = 0; j < 9; j++){
 9                 if(board[i][j] == '.') continue;
10                 int n = board[i][j] - '1';
11                 if(row[i][n] || col[j][n] || matrix[i - i % 3 + j / 3][n]){
12                     return false;
13                 }
14                 row[i][n] = col[j][n] = matrix[i - i % 3 + j / 3][n] = true;
15                 
16             }
17         }
18         return true;
19     }
20 }