sudoku_engine.py

import numpy as np
'''
1.Check if board is full or not
2.Find first empty space 
3.Put number from 1-9 in it
3a.Check if it is only number in row column 3x3 subboard aka if number is valid
4.If number is not legal make place empty
5.Repeate 1,2,3.
'''
board = [[0 for x in range(1,10)] for y in range(1,10)] 
board = [[3,0,6,5,0,8,4,0,0],
        [5,2,0,0,0,0,0,0,0],
        [0,8,7,0,0,0,0,3,1],
        [0,0,3,0,1,0,0,8,0],
        [9,0,0,8,6,3,0,0,5],
        [0,5,0,0,9,0,6,0,0],
        [1,3,0,0,0,0,2,5,0],
        [0,0,0,0,0,0,0,7,4],
        [0,0,5,2,0,6,3,0,0]]


def pretty_printed(board):
    for r in range(len(board)):
        if r%3==0 and r!=0:
            print('-------------------')
        for c in range(len(board[r])):
            if c%3==0 and c!=0:
                print('|',end='')
            if c == 8:
                print(board[r][c])
            else:
                print(str(board[r][c])+' ' ,end='')


def empty_space(board):
    for r in range(len(board)):
        for c in range(len(board[r])):
            if board[r][c] == 0:
                return (r,c)
    return None


def valid_n(board,n,r,c):
    for i in range(len(board)):
        #column
        if n == board[i][c]:
            return False
        #row
        if n == board[r][i]: 
            return False

    r_ = r//3
    c_ = c//3
    for r in range(r_*3,r_*3+3):
        for c in range(c_*3,c_*3+3):
            if n == board[r][c]:
                return False

    return True
    

def sudoku_solver(board):
    if not empty_space(board):  #if you dont find empty space return True because if function is true that mean  
        return True 
    else:                       #if you find empty space proceed to occupied it with number                         
        r,c = empty_space(board)
    for n in range(1,10):
        if valid_n(board,n,r,c):  #if number is safe put it in place.
            board[r][c] = n
            if sudoku_solver(board):
                return True
            board[r][c] = 0 
    return False


def random_zeros(board):
    counter = 0
    while counter <= 40:
        counter += 1
        r = int(np.random.choice(9,1))
        c = int(np.random.choice(9,1))
        board[r][c] = 0


if __name__ == '__main__':
    sudoku_solver(board)
    random_zeros(board)
    pretty_printed(board)