Getting a list of 3 by 3 boxes in a Sudoku puzzle

user_18063085 0
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Assuming the sudoku puzzle is a 9 by 9 and is filled with 0-9. I want is 9 lists, with each list containing a 3 by 3 Sudoku box.

This is what I have:

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

list1 = []
for i in range(0,3):
    for j in range(0,3):
        list1.append(grid[i][j])

 list2 = []
for i in range(0,3):
    for j in range(4,7):
        list2.append(grid[i][j])

and it goes on and on.......

How do I simplify this for loop for getting a list of 3 by 3 boxes in Sudoku puzzle?

sudoku list python
2 Answers

You need to add a step parameter to your range()s so that you start reading in each box at the appropriate row / column index:

from itertools import product
boxes = []
for row_start, col_start in product(range(0, 9, 3), repeat=2):
    boxes.append([
            [grid[row][col] for col in range(col_start, col_start + 3)]
            for row in range(row_start, row_start + 3)
        ])

print(boxes)

This outputs:

[
 [[5, 0, 0], [0, 1, 0], [0, 0, 0]],
 [[0, 0, 0], [0, 8, 7], [0, 0, 3]],
 [[0, 0, 1], [0, 6, 0], [0, 0, 0]],
 [[0, 5, 0], [0, 0, 2], [0, 0, 0]],
 [[0, 6, 1], [0, 0, 0], [4, 0, 0]],
 [[0, 7, 0], [9, 0, 0], [0, 0, 0]],
 [[0, 0, 0], [9, 0, 0], [0, 8, 0]],
 [[5, 0, 0], [0, 4, 8], [3, 0, 0]],
 [[0, 4, 0], [7, 0, 0], [0, 0, 0]]
]
user_177698150 
from pprint import pprint as pp

SIZE = 3

sudoku = [[[0] * SIZE for _ in range(SIZE)] for _ in range(SIZE * SIZE)]

# example of populating it
for i in range(SIZE):
    for j in range(SIZE):
        counter = i * SIZE + j
        sudoku[counter][i][j] = counter + 1

pp(sudoku)

output

[[[1, 0, 0], [0, 0, 0], [0, 0, 0]],
 [[0, 2, 0], [0, 0, 0], [0, 0, 0]],
 [[0, 0, 3], [0, 0, 0], [0, 0, 0]],
 [[0, 0, 0], [4, 0, 0], [0, 0, 0]],
 [[0, 0, 0], [0, 5, 0], [0, 0, 0]],
 [[0, 0, 0], [0, 0, 6], [0, 0, 0]],
 [[0, 0, 0], [0, 0, 0], [7, 0, 0]],
 [[0, 0, 0], [0, 0, 0], [0, 8, 0]],
 [[0, 0, 0], [0, 0, 0], [0, 0, 9]]]
user_300380
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