Building a Sudoku Solver - Step 43,44

Python
1

in step 43, you are asked to print the gameboard.value_in_square(1, 0, 3). My question is, how is row 1 the first 3 rows; why isn’t it row 0? Column 0 is the first 3 columns, which makes sense because (col // 3) * 3 should = 0 for 0, 1, and 2… how is this not the same for (row // 3 * 3)?

2

I’m not understanding your question. Can you please post a link to the step and any code you currently have?

3

Here’s the code (step 43)…

class Board:
    def __init__(self, board):
        self.board = board

    def find_empty_cell(self):
        for row, contents in enumerate(self.board):
            try:
                col = contents.index(0)
                return row, col
            except ValueError:
                pass
        return None

    def valid_in_row(self, row, num):
        return num not in self.board[row]

    def valid_in_col(self, col, num):
        return all(self.board[row][col] != num for row in range(9))

    def valid_in_square(self, row, col, num):
        row_start = (row // 3) * 3
        col_start = (col // 3) * 3
        for row_no in range(row_start, row_start + 3):
            for col_no in range(col_start, col_start + 3):
                if self.board[row_no][col_no] == num:
                    return False
        return True

puzzle = [
  [0, 0, 2, 0, 0, 8, 0, 0, 0],
  [0, 0, 0, 0, 0, 3, 7, 6, 2],
  [4, 3, 0, 0, 0, 0, 8, 0, 0],
  [0, 5, 0, 0, 3, 0, 0, 9, 0],
  [0, 4, 0, 0, 0, 0, 0, 2, 6],
  [0, 0, 0, 4, 6, 7, 0, 0, 0],
  [0, 8, 6, 7, 0, 4, 0, 0, 0],
  [0, 0, 0, 5, 1, 9, 0, 0, 8],
  [1, 7, 0, 0, 0, 6, 0, 0, 5]
]

gameboard = Board(puzzle)
print(gameboard.valid_in_square(1, 0, 3))

In this code, the first square is being iterated through… but I thought the first square should have been (0, 0, num).

4

Can you please post a link to the step?

5

Building a Sudoku step 43

6

How familiar are you with Sudoku?

The first square is the 9 values in rows 0,1,2 and columns 0,1,2.

7

I’m familiar and I agree with your statement. My question is still the same. Why is it accessed as square(1, 0, num) and not square(0, 0, num)?
row_start = (row // 3) * 3, right? For rows 0,1,2, row_start = 0, right?

8

where do you see square(1, 0, num)?

9

Okay, I get it now… the square is accessable using 0, 1, or 2 for both rows or columns… so square(1,2,num) is also the first square… and the 9th square can be accessed by square(8,7,num).

1 Like
10

exactly this

11

in step 43, they tell you to print gameboard.valid_in_square(1,0,3). The point is to check for the (num)ber 3 in the upper left square. That square can be acessed from (0,0,num) through (2,2,num). The (1,0,num) threw me off for a minute, obviously.

12

oh, that is confusing, I was searching for a method or function called square, instead you meant the one called valid_in_square!

13

I just meant the first, upper left square.