Generate shuffed 9x9 sudoku

sudoku_generator.py

"""
Sudoku generator

Algorithm shamelessly borrowed from https://stackoverflow.com/a/56581709/16747758 (By Alain T., released under CC-BY-SA 4.0)
"""
from itertools import product, batched, chain
from typing import *
from random import sample


def check_sudoku_valid(board) -> (bool, str):
	"""
	Check if the sudoku board is a valid board.
	Note that a non-full board can be a valid board.
	"""
	
	# Check rows
	for row_index, row in enumerate(board):
		row_used: list = []
		for cell in row:
			if cell in row_used:
				return False, f'Value {cell} repeated in row {row_index}'
			row_used.append(cell)
	# Check columns
	for column_index in range(9):
		column_used: list = []
		for row_index in range(9):
			cell = board[row_index][column_index]
			if cell in column_used:
				return False, f'Value {cell} repeated in column {column_index}'
			column_used.append(cell)
	# Check boxes
	for i, j in product(range(3), repeat=2):
		box_used: list = []
		for k, l in product(range(3), repeat=2):
			cell = board[i * 3 + k][j * 3 + l]
			if cell in box_used:
				return False, f'Value {cell} repeated in box {3 * i + j}'
			box_used.append(cell)
	return True


def generate_shuffled_board(board: list[list[int]] = None, shuffle_times: int = 5) -> list[list[int]]:
	if board is None:
		board: list[list[int]] = [
			[1, 2, 3, 4, 5, 6, 7, 8, 9],
			[4, 5, 6, 7, 8, 9, 1, 2, 3],
			[7, 8, 9, 1, 2, 3, 4, 5, 6],
			[2, 3, 1, 5, 6, 4, 8, 9, 7],
			[5, 6, 4, 8, 9, 7, 2, 3, 1],
			[8, 9, 7, 2, 3, 1, 5, 6, 4],
			[3, 1, 2, 6, 4, 5, 9, 7, 8],
			[6, 4, 5, 9, 7, 8, 3, 1, 2],
			[9, 7, 8, 3, 1, 2, 6, 4, 5]
		]
	assert check_sudoku_valid(board)
	# Shuffle row group
	row_grouped = list(batched(board, 3))
	row_grouped = sample(row_grouped, 3)
	board = list(chain.from_iterable(row_grouped))
	assert check_sudoku_valid(board)
	# Shuffle row 1-3
	shuffled_rows = sample(board[0:3], 3)
	board = [*shuffled_rows, *board[3:]]
	assert check_sudoku_valid(board)
	# Shuffle row 4-6
	shuffled_rows = sample(board[3:6], 3)
	board = [*board[0:3], *shuffled_rows, *board[6:9]]
	assert check_sudoku_valid(board)
	# Shuffle row 7-9
	shuffled_rows = sample(board[6:9], 3)
	board = [*board[0:6], *shuffled_rows]
	assert check_sudoku_valid(board)
	# Row <-> Column
	board = list(zip(*board))
	assert check_sudoku_valid(board)
	# Shuffle row group
	row_grouped = list(batched(board, 3))
	row_grouped = sample(row_grouped, 3)
	board = list(chain.from_iterable(row_grouped))
	assert check_sudoku_valid(board)
	# Shuffle row 1-3
	shuffled_rows = sample(board[0:3], 3)
	board = [*shuffled_rows, *board[3:]]
	assert check_sudoku_valid(board)
	# Shuffle row 4-6
	shuffled_rows = sample(board[3:6], 3)
	board = [*board[0:3], *shuffled_rows, *board[6:9]]
	assert check_sudoku_valid(board)
	# Shuffle row 7-9
	shuffled_rows = sample(board[6:9], 3)
	board = [*board[0:6], *shuffled_rows]
	assert check_sudoku_valid(board)
	# Column <-> Row
	board = list(zip(*board))
	assert check_sudoku_valid(board)
	
	for _ in range(shuffle_times-1):
		print(board)
		board = generate_shuffled_board(board)
	
	return board


for line in generate_shuffled_board():
	print(line)