36. 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.

 分析 ： 3 个hashset

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