leetcode : 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.

 

tag :  HashSet 、  add 操作 及返回值。  

if(board[i][j] != '.' && !rows.add(board[i][j])) {
return false;
}

此行代码： 先做了添加操作，再返回的值，所以 二者合一。

另外：  而为矩阵的行列转换技巧  除法和求余数

public class Solution {
    public boolean isValidSudoku(char[][] board) {
        
        for(int i = 0; i < 9 ;i++) {
            HashSet<Character> rows = new HashSet<Character>();
            HashSet<Character> cols = new HashSet<Character>();
            HashSet<Character> cube = new HashSet<Character>();
            
            for(int j = 0; j < 9; j++) {
                //row
                if(board[i][j] != '.' && !rows.add(board[i][j])) {
                    return false;
                }
                if(board[j][i] != '.' && !cols.add(board[j][i])) {
                    return false;
                }
                int row = 3*(i/3);
                int col = 3*(i%3);
                 if(board[row + j/3][col + j%3]!='.' && !cube.add(board[row + j/3][col + j%3]))
                return false;
            }
        }
        return true;
    }
}