Question: https://leetcode.com/problems/valid-sudoku/description/

I divided there problem in 3 parts:

1. check all rows
2. check all columns
3. check all the 3x3 grid

checking rows and columns would be done by this method:

# same logic would be used to see if row/column is valid or not.
    def isValidRC(self, row_col: List[str]) -> bool:
        temp = set()
        for i in row_col:
            if i != '.':
                if i in temp:
                    return False
                temp.add(i)
        return True

For fetching rows:

# check all the rows
        for row in board:
            if not self.isValidRC(row):
                return False

For fetching columns:

# check all the columns
        for i in range(9):
            col = [row[i] for row in board]
            if not self.isValidRC(col):
                return False

For checking 3x3 grids I created 2 methods:

def isValid3x3(self, sub):
        temp = set()
        for row in sub:
            for ele in row:
                if ele != '.':
                    if ele in temp:
                        return False
                    temp.add(ele)
        return True
        
    def get3x3(self,board,*n):
        sub = []
        for rno in range(n[0],n[1]):
            row = board[rno][n[2]:n[3]]
            sub.append(row)
        if not self.isValid3x3(sub):
            return False
        return True
        

I checked all the 3x3 like this:

# check all the 3x3 sub boards
        # first 3x3
        if not self.get3x3(board,0,3,0,3):
            return False
        
        # second 3x3
        if not self.get3x3(board,0,3,3,6):
            return False
        
        # third 3x3
        if not self.get3x3(board,0,3,6,9):
            return False
        
        # fourth 3x3
        if not self.get3x3(board,3,6,0,3):
            return False
        
        # fifth 3x3
        if not self.get3x3(board,3,6,3,6):
            return False
        
        # sixth 3x3
        if not self.get3x3(board,3,6,6,9):
            return False
        
        # seventh 3x3
        if not self.get3x3(board,6,9,0,3):
            return False
        
        # eighth 3x3
        if not self.get3x3(board,6,9,3,6):
            return False
        # ninth 3x3
        if not self.get3x3(board,6,9,6,9):
            return False

I know this is a brute-force solution. But I have already spent more than 4 hours today. And I have a lot of other tasks to complete.

Final solution:

class Solution:
    # same logic would be used to see if row/column is valid or not.
    def isValidRC(self, row_col):
        temp = set()
        for i in row_col:
            if i != '.':
                if i in temp:
                    return False
                temp.add(i)
        return True
    def isValid3x3(self, sub):
        temp = set()
        for row in sub:
            for ele in row:
                if ele != '.':
                    if ele in temp:
                        return False
                    temp.add(ele)
        return True
    def get3x3(self,board,*n):
        sub = []
        for rno in range(n[0],n[1]):
            row = board[rno][n[2]:n[3]]
            sub.append(row)
        if not self.isValid3x3(sub):
            return False
        return True

    def isValidSudoku(self, board: List[List[str]]) -> bool:
        # check all the rows
        for row in board:
            if not self.isValidRC(row):
                return False
        # check all the columns
        for i in range(9):
            col = [row[i] for row in board]
            if not self.isValidRC(col):
                return False            
        # check all the 3x3 sub boards
        # first 3x3
        if not self.get3x3(board,0,3,0,3):
            return False
        
        # second 3x3
        if not self.get3x3(board,0,3,3,6):
            return False
        
        # third 3x3
        if not self.get3x3(board,0,3,6,9):
            return False
        
        # fourth 3x3
        if not self.get3x3(board,3,6,0,3):
            return False
        
        # fifth 3x3
        if not self.get3x3(board,3,6,3,6):
            return False
        
        # sixth 3x3
        if not self.get3x3(board,3,6,6,9):
            return False
        
        # seventh 3x3
        if not self.get3x3(board,6,9,0,3):
            return False
        
        # eighth 3x3
        if not self.get3x3(board,6,9,3,6):
            return False
        # ninth 3x3
        if not self.get3x3(board,6,9,6,9):
            return False
        
        return True