Super Simple Sudoku Solver in Python

rySudoku01.py

'''
rySudoku01.py

Super Simple Sudoku Solver in Python

http://code.activestate.com/recipes/578140-super-simple-sudoku-solver-in-python-source-code/

Takes a partially filled in grid, inserts the min value in a cell (could be a random cell, in this case the first free cell). 

If the min value is not legal it will increment until the max value is reached (number 9), checking each time if the incremented value is legal in that cell (ie does not clash with any already entered cells in square, col or row). 

If it is legal, it will call itself (the hasSolution function) thus using this slightly more filled in grid to find a new cell and check which value is legal in this next cell. 

If no values are legal in the next cell, it will clear the previous grid entry and try incrementing the value.

isLegal = does not conflict with any other numbers in the same row, column or square

'''

import re 
import random 
import os

# GLOBAL VARIABLES 
grid_size = 81

def isFull (grid):     
  return grid.count('.') == 0
  
# can be used more purposefully
def getTrialCelli(grid):
  for i in range(grid_size):
    if grid[i] == '.':
      print('trial cell', i)
      return i
      
def isLegal(trialVal, trialCelli, grid):

  cols = 0
  for eachSq in range(9):
    
    trialSq=  [ x+cols for x in range(3) ] 
    trialSq+= [ x+9+cols for x in range(3) ] 
    trialSq+= [ x+18+cols for x in range(3) ]
    
    cols +=3
    if cols in [9, 36]:
      cols +=18
    if trialCelli in trialSq:
      for i in trialSq:
        if grid[i] != '.':
          if trialVal == int(grid[i]):
            print('SQU', end=' ')
            return False
  
  for eachRow in range(9):
    trialRow = [ x+(9*eachRow) for x in range (9) ]
    if trialCelli in trialRow:
      for i in trialRow:
        if grid[i] != '.':
          if trialVal == int(grid[i]):
            print('ROW', end=' ')
            return False
  
  for eachCol in range(9):
    trialCol = [ (9*x)+eachCol for x in range (9) ]
    if trialCelli in trialCol:
      for i in trialCol:
        if grid[i] != '.':
          if trialVal == int(grid[i]):
            print('COL', end=' ')
            return False
  print('is legal', 'cell',trialCelli, 'set to ', trialVal)
  return True

def setCell(trialVal, trialCelli, grid):
  grid[trialCelli] = trialVal
  return grid

def clearCell( trialCelli, grid ):
  grid[trialCelli] = '.'
  print('clear cell', trialCelli)
  return grid


def hasSolution (grid):
  if isFull(grid):
    print('\nSOLVED')
    return True
  else:
    trialCelli = getTrialCelli(grid)
    trialVal = 1
    solution_found = False
    while ( solution_found != True) and (trialVal < 10):
      print('trial valu',trialVal, end=' ')
      if isLegal(trialVal, trialCelli, grid):
        grid = setCell(trialVal, trialCelli, grid)
        if hasSolution (grid) == True:
          solution_found = True
          return True
        else:
          clearCell( trialCelli, grid )
      print('++')
      trialVal += 1
  return solution_found



def printGrid (grid, add_zeros):
  i = 0
  for val in grid:
    if add_zeros == 1:
      if int(val) < 10: 
        print('0'+str(val), end=' ')
      else:
        print(val, end=' ')
    else:
        print(val, end=' ')
    i +=1
    
    trialSq= [ (x*9)+3 for x in range(81)] 
    trialSq+=[ (x*9)+6 for x in range(81)] 
    trialSq+=[ (x*9)+9 for x in range(81)] 

    if i in trialSq:
        print('|', end=' ')
    
    if add_zeros == 1:
      if i in [ 27, 54, 81]:
        print('\n---------+----------+----------+')
      elif i in [ (x*9) for x in range(81)]:
        print('\n')
    else:
      if i in [ 27, 54, 81]:
        print('\n------+-------+-------+')
      elif i in [ (x*9) for x in range(81)]:
        print('\n')

def main ():

  #sampleGrid = ['2', '1', '.', '.', '.', '.', '.', '.', '.', '.', '.', '.', '.', '.', '3', '1', '.', '.', '.', '.', '9', '4', '.', '.', '.', '.', '7', '8', '2', '5', '.', '.', '4', '.', '.', '.', '.', '.', '.', '6', '.', '.', '.', '.', '.', '1', '.', '.', '.', '.', '8', '2', '.', '.', '.', '7', '.', '.', '9', '.', '.', '.', '.', '.', '.', '.', '.', '3', '1', '.', '4', '.', '.', '.', '.', '.', '.', '.', '3', '8', '.']
  
  #sampleGrid = ['.', '.', '3', '.', '2', '.', '6', '.', '.', '9', '.', '.', '3', '.', '5', '.', '.', '1', '.', '.', '1', '8', '.', '6', '4', '.', '.', '.', '.', '8', '1', '.', '2', '9', '.', '.', '7', '.', '.', '.', '.', '.', '.', '.', '8', '.', '.', '6', '7', '.', '8', '2', '.', '.', '.', '.', '2', '6', '.', '9', '5', '.', '.', '8', '.', '.', '2', '.', '3', '.', '.', '9', '.', '.', '5', '.', '1', '.', '3', '.', '.']
  
  sampleGrid = ['.', '.', '.', '.', '.', '.', '.', '.', '.', '.', '.', '.', '.', '.', '.', '.', '.', '.', '.', '.', '.', '.', '.', '.', '.', '.', '.', '.', '.', '.', '.', '.', '.', '.', '.', '.', '.', '.', '4', '6', '2', '9', '5', '1', '8', '1', '9', '6', '3', '5', '8', '2', '7', '4', '4', '7', '3', '8', '9', '2', '6', '5', '1', '6', '8', '.', '.', '3', '1', '.', '4', '.', '.', '.', '.', '.', '.', '.', '3', '8', '.']
  
  printGrid(sampleGrid, 0)

  if hasSolution (sampleGrid):
    printGrid(sampleGrid, 0)
  
  else: print('NO SOLUTION')

  
if __name__ == "__main__":
    main()

#
# 執行結果
#

'''
$ python3 rySudoku01.py

. . . | . . . | . . . | 

. . . | . . . | . . . | 

. . . | . . . | . . . | 
------+-------+-------+
. . . | . . . | . . . | 

. . 4 | 6 2 9 | 5 1 8 | 

1 9 6 | 3 5 8 | 2 7 4 | 
------+-------+-------+
4 7 3 | 8 9 2 | 6 5 1 | 

6 8 . | . 3 1 | . 4 . | 

. . . | . . . | 3 8 . | 
------+-------+-------+

SOLVED
2 1 5 | 4 6 3 | 8 9 7 | 

3 4 7 | 9 8 5 | 1 2 6 | 

8 6 9 | 2 1 7 | 4 3 5 | 
------+-------+-------+
5 2 8 | 1 7 4 | 9 6 3 | 

7 3 4 | 6 2 9 | 5 1 8 | 

1 9 6 | 3 5 8 | 2 7 4 | 
------+-------+-------+
4 7 3 | 8 9 2 | 6 5 1 | 

6 8 2 | 5 3 1 | 7 4 9 | 

9 5 1 | 7 4 6 | 3 8 2 | 
------+-------+-------+ 
'''