CreateSudokus_v2

import itertools
import numpy as np
import random
import time

def possible(board,num,row,col, printReason=False):

    # check row
    for i in range(9):
        if board[row, i] == num:
            if printReason:
                print(f"{num} tested at {row},{col} --> already in the same row (at col {i})")
            return False
    # check column
    for i in range(9):
        if board[i, col] == num:
            if printReason:
                print(f"{num} tested at {row},{col} --> already in the same col (at row {i})")
            return False
    # check square
    row0 = (row//3)*3
    col0 = (col//3)*3
    for y in range(row0, row0+3):
        for x in range(col0, col0+3):
            if board[y,x] == num:
                if printReason:
                    print(f"{num} tested at {row},{col} --> already in the same square (at square with upper left corner {row0}, {col0})")
                return False
    return True

def solveSudoku(board, random_nums, onlyFirstSolution, suppress_print):

    global counter

    for row in range(9):
        for col in range(9):
            if board[row,col] == 0:
                nums1to9 = np.arange(1,10)
                if random_nums:
                    random.shuffle(nums1to9)
                for num in nums1to9:
                    if possible(board, num, row, col):
                        board[row,col] = num
                        solveSudoku(board,random_nums,onlyFirstSolution,suppress_print)
                        board[row,col] = 0 # try new possibilities (non-unique Sudoku)
                return # backtracking (empty field, but no number fits) --> does not print out the "wrong" Sudoku

    counter += 1

    if not suppress_print:
        # Check if Sudoku is the same
        if counter == 1:
            try:
                if np.array_equal(first_sudoku, board):
                    print("Sudoku is not solvable/over-constrained!")
                    return
            except:
                print("Define the variable first_sudoku.")

    if onlyFirstSolution:
        return board

    if not suppress_print:
        print(f"Solution #{counter}:\n")
        print(board, "\n")

    if onlyFirstSolution:
        return board

    ## PREVENT CPU OVERLOAD ##
    if counter > 100:
        return

    return board

def createSudoku():

    global counter
    global first_sudoku

    sudoku = np.zeros((9,9))
    first_sudoku = sudoku.copy()
    counter = 0
    sudoku = solveSudoku(board=first_sudoku, random_nums=True, onlyFirstSolution=True, suppress_print=True)
    print("---")
    print(sudoku)
    print("----")
    ## user selects difficulty level
    while True:
        numClues_input = input("Choose difficulty level:\n1) Extremely easy\n2) Easy\n3) Medium\n4) Difficult\n5) Evil\n\n--> ")
        if numClues_input.lower() in ["1", "1)", "one", "eins", "i", "extremely easy"]:
            numClues = random.randint(47,80)
            break
        elif numClues_input.lower() in ["2", "2)", "two", "zwei", "ii", "easy"]:
            numClues = random.randint(36,46)
            break
        elif numClues_input.lower() in ["3", "3)", "three", "drei", "iii", "medium"]:
            numClues = random.randint(32,35)
            break
        elif numClues_input.lower() in ["4", "4)", "four", "vier", "iv", "difficult"]:
            numClues = random.randint(28,31)
            break
        elif numClues_input.lower() in ["5", "5)", "five", "fünf", "v", "evil"]:
            numClues = random.randint(17,27)
            break
        print("\nSelect difficulty level...\n")

    print(f"\nYou have selected difficulty level {numClues_input}. Therefore you will get {numClues} clues.")

    numRemoveClues = 81-numClues

    ## remove up to 81-17=64 clues until there is a unique solution
    allCoordinates = list(itertools.product(range(0,9), repeat=2))

    while_counter = 0
    start = time.time()
    while True:
        removeCoordinates = random.choices(allCoordinates, k=numRemoveClues)
        for coord in removeCoordinates:
            row = coord[0]
            col = coord[1]
            sudoku[row, col] = 0
        counter = 0
        sudoku = solveSudoku(board=first_sudoku, random_nums=True, onlyFirstSolution=False, suppress_print=True)
        if counter == 1:
            return sudoku

        while_counter += 1
        if while_counter in [10,100,1000,10000,100000,1000000]:
            print(f"{while_counter} Sudokus with {numClues} clues have been found so far, but none of them is unique...")
        stop = time.time()
        elapsed_time = stop-start
        if elapsed_time > 120:
            print("Time elapsed has exceed the maximum waiting time of 120s.")
            break