[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：

public class Solution {
    public boolean isValidSudoku(char[][] board) {
        if(board == null || board.length != 9 || board[0].length != 9) return false;
        boolean[][] row = new boolean[9][9];
        boolean[][] col = new boolean[9][9];
        boolean[][] matrix = new boolean[9][9];
        for(int i = 0; i < 9; i++){
            for(int j = 0; j < 9; j++){
                if(board[i][j] == '.') continue;
                int n = board[i][j] - '1';
                if(row[i][n] || col[j][n] || matrix[i - i % 3 + j / 3][n]){
                    return false;
                }
                row[i][n] = col[j][n] = matrix[i - i % 3 + j / 3][n] = true;
                
            }
        }
        return true;
    }
}