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.

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思路： 就是检查一遍里面的每个点是否合法.

易错点： 别忘了排除 同一个位置的。

public class Solution {
    public boolean isValidSudoku(char[][] board) {
        for(int i = 0; i < 9; i++){
            for(int j = 0; j < 9; j++){
                if(board[i][j] != '.'){
                    if(!isValid(board, i, j))
                        return false;
                }
            }
        }
        return true;
    }
    
    private boolean isValid(char[][] board, int x, int y){
        char c = board[x][y];
        for(int i = 0; i < 9; i++){
            if(i != y && board[x][i] == c)
                return false;
            if(i != x && board[i][y] == c)
                return false;
            int blockRow = 3 * (x / 3) + i / 3;
            int blockCol = 3 * (y / 3) + i % 3;
            if((blockRow != x || blockCol != y) && board[blockRow][blockCol] == c)
                return false;
        }
        return true;
    }
}