[leetcode 36] Valid Sudoku

Determine if a 9 x 9 Sudoku board is valid. Only the filled cells need to be validated according to the following rules:

1. Each row must contain the digits 1-9 without repetition.
2. Each column must contain the digits 1-9 without repetition.
3. Each of the nine 3 x 3 sub-boxes of the grid must contain the digits 1-9 without repetition.

Note:

• A Sudoku board (partially filled) could be valid but is not necessarily solvable.
• Only the filled cells need to be validated according to the mentioned rules.

 

Example 1:

Input: board = [["5","3",".",".","7",".",".",".","."] ,["6",".",".","1","9","5",".",".","."] ,[".","9","8",".",".",".",".","6","."] ,["8",".",".",".","6",".",".",".","3"] ,["4",".",".","8",".","3",".",".","1"] ,["7",".",".",".","2",".",".",".","6"] ,[".","6",".",".",".",".","2","8","."] ,[".",".",".","4","1","9",".",".","5"] ,[".",".",".",".","8",".",".","7","9"]] Output: true

Example 2:

Input: board = [["8","3",".",".","7",".",".",".","."] ,["6",".",".","1","9","5",".",".","."] ,[".","9","8",".",".",".",".","6","."] ,["8",".",".",".","6",".",".",".","3"] ,["4",".",".","8",".","3",".",".","1"] ,["7",".",".",".","2",".",".",".","6"] ,[".","6",".",".",".",".","2","8","."] ,[".",".",".","4","1","9",".",".","5"] ,[".",".",".",".","8",".",".","7","9"]] Output: false Explanation: Same as Example 1, except with the 5 in the top left corner being modified to 8. Since there are two 8's in the top left 3x3 sub-box, it is invalid.

 

Constraints:

• board.length == 9
• board[i].length == 9
• board[i][j] is a digit or '.'.

class Solution {
    
    char[][] b;

    public boolean check(int row, int col){
        int[] cflag = new int[10];
        int[] rflag = new int[10];
        int[] bflag = new int[10];
        
        
        for(int i=0; i<9; i++){
            if(b[i][col] != '.'){
                cflag[b[i][col]-'0']++;
                if(cflag[b[i][col]-'0'] > 1){
                    return false;
                }
            }
            
             if(b[row][i] != '.'){
                rflag[b[row][i]-'0']++;
                if(rflag[b[row][i]-'0'] > 1){
                    return false;
                }
            }
        }
        
        int r = row/3;
        int c = col/3;
        
        for(int i=0; i<3; i++){
            for(int j=0; j<3; j++){

                if(b[r*3 + i][c*3 + j] != '.'){
                    bflag[b[r*3 + i][c*3 + j]-'0']++;
                    if(bflag[b[r*3 + i][c*3 + j]-'0'] > 1){
                        return false;
                    }
                }
            }
        }
        return true;
    }
    

    public boolean isValidSudoku(char[][] board) {
        
        b = board;
        
        for(int i=0; i<9; i++){
            for(int j=0; j<9; j++){
                if(!check(i,j)){
                    return false;
                }
            }
        }
        
        return true;
    }
}