Home/ Questions/Q 3785
Next
In Process

askthedev.com Latest Questions

Asked: 2024-09-24T18:16:00+05:30 In:

You are given a 9×9 grid that represents a Sudoku board. The objective is to determine whether the board is valid according to the following rules: 1. Each row must contain the digits 1-9 at most once. 2. Each column must contain the digits 1-9 at most once. 3. Each of the nine 3×3 sub-boxes that divide the grid must also contain the digits 1-9 at most once. The board may include empty cells represented by the character ‘.’ which means that the cell contains no value. Your task is to write a function that checks if the given Sudoku board configuration adheres to these constraints, effectively verifying its validity.

Have you ever tried solving Sudoku puzzles? They’re a brain workout, right? But let me flip that around a little: instead of solving, what if you had to check if a given Sudoku board is valid? It might seem straightforward, but there are a few tricky rules to keep in mind.

Imagine you’ve got a classic 9×9 Sudoku grid in front of you. Each row, column, and the nine 3×3 sub-grids within the grid must have the numbers 1 through 9 appear exactly once. But here’s the catch: some cells might be empty, represented by a dot (.). Your task is to verify if the numbers that do appear fit into these constraints correctly, even with those empty spots.

Let me give you an example. Picture a board that looks like this:

“`
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
“`

So, if you were to analyze this board, what would you look for? You’d want to make sure that each row doesn’t repeat any numbers from 1 to 9 more than once. The same goes for the columns and each of those little 3×3 boxes.

Now, how would you tackle that? Would you use a bunch of temporary lists or sets to track what you’ve seen? It sounds simple enough, but there’s a lot to keep track of, and it’s easy to miss something, especially with all those dots floating around.

If you think you can write a function to check if this board configuration is valid according to the Sudoku rules, what logic would you implement? Would you traverse the board in a specific order or use nested loops? Keep in mind that it’s not just about spotting duplicates—you’ve got to be systematic about checking all three areas: rows, columns, and 3×3 boxes. Give it a shot and see how you would approach validating the Sudoku board!

Share

    Leave an answer

    You must login to add an answer.

    Need An Account,

    2 Answers






    1. Sudoku Validity Checker

      Sudoku Validity Checker

      So, checking if a Sudoku board is valid sounds like a fun challenge! I mean, it’s all about making sure that every number from 1 to 9 is used correctly, right? Here’s how I would think about tackling it:

      Steps to Check the Sudoku Board

      1. Create some containers: I guess I’ll need lists or sets to keep track of the numbers I see as I go through the board. One set for each row, one for each column, and one for each of the 3×3 boxes.
      2. Loop through the board: I think I’d use two nested loops. One for rows and one for columns—like, a double loop, where the outer one goes through the rows (0 to 8) and the inner one goes through the columns (also 0 to 8).
      3. Check each cell: Inside those loops, I’d check if the cell is empty (i.e., it’s a dot). If it’s not empty, I’d look at the number. Then, I’d check if it’s already in the respective row, column, or box set.
      4. Add numbers to sets: If it’s not a repeat, I’d add it to its corresponding row, column, and box set.
      5. Return false if duplicates: If I find any duplicates while checking, I would just return false immediately.
      6. Finish up: If I go through the entire board without finding any problems, then I’d return true for a valid board!

      Example Code (Like My First Attempt)

              
def isValidSudoku(board):
    rows = [set() for _ in range(9)]
    columns = [set() for _ in range(9)]
    boxes = [set() for _ in range(9)]
    
    for r in range(9):
        for c in range(9):
            num = board[r][c]
            if num != '.':
                box_index = (r // 3) * 3 + (c // 3)
                if (num in rows[r] or num in columns[c] or num in boxes[box_index]):
                    return False
                rows[r].add(num)
                columns[c].add(num)
                boxes[box_index].add(num)
    return True

      So, yeah, that’s how I’d try to check a Sudoku board! It might be a bit messy, but I think it would work. And it’s all about keeping track of the numbers, right? Hope this makes sense!


    2. To validate a given Sudoku board, we need to ensure that each number from 1 to 9 appears exactly once in each row, column, and 3×3 sub-grid. This can be achieved by using three sets for tracking the seen numbers in rows, columns, and boxes. As we traverse the Sudoku grid, we can iterate through each cell. If the cell contains a number, we check whether that number has already been encountered in the corresponding row set, column set, or box set. If we find a duplicate, we return false immediately. If there are no duplicates for the entire traversal, we confirm the board is valid.

      To implement this logic, a systematic approach using nested loops is effective. The outer loop iterates through each cell in the 9×9 grid while the inner logic handles the detection of duplicates. For each position (i, j), we calculate the index of the 3×3 box by using integer division (box_row = i // 3 and box_col = j // 3). This way, we can maintain clean criteria for checking legality in all three areas. The handling of empty cells represented by dots (.) should be straightforward: if we encounter a dot, we simply continue without any checks. After completing the validation for all cells, we can confidently declare if the Sudoku board is valid or not.

    Related Questions