24 game/Solve

Write a function that given four digits subject to the rules of the 24 game, computes an expression to solve the game if possible.

Show examples of solutions generated by the function

Python

The function is called solve, and is integrated into the game player. The docstring of the solve function shows examples of its use when isolated at the Python command line. <lang Python>

The 24 Game Player

Given any four digits in the range 1 to 9, which may have repetitions,
Using just the +, -, *, and / operators; and the possible use of
brackets, (), show how to make an answer of 24.

An answer of "q" will quit the game.
An answer of "!" will generate a new set of four digits.
An answer of "?" will compute an expression for the current digits.

Otherwise you are repeatedly asked for an expression until it evaluates to 24

Note: you cannot form multiple digit numbers from the supplied digits,
so an answer of 12+12 when given 1, 2, 2, and 1 would not be allowed.

from __future__ import division, print_function from itertools import permutations, combinations, product, zip_longest, \

                        chain

from pprint import pprint as pp import random, ast, re import sys

if sys.version_info[0] < 3: input = raw_input

def choose4():

   'four random digits >0 as characters'
   return [str(random.randint(1,9)) for i in range(4)]

def welcome(digits):

   print (__doc__)
   print ("Your four digits: " + ' '.join(digits))

def check(answer, digits):

   allowed = set('() +-*/\t'+.join(digits))
   ok = all(ch in allowed for ch in answer) and \
        all(digits.count(dig) == answer.count(dig) for dig in set(digits)) \
        and not re.search('\d\d', answer)
   if ok:
       try:
           ast.parse(answer)
       except:
           ok = False
   return ok

def solve(digits):

   """\
   >>> solve(list('3246'))
   Solution found: 2 + 3 * 6 + 4
   '2 + 3 * 6 + 4'
   >>> solve(list('4788'))
   Solution found: ( 4 + 7 - 8 ) * 8
   '( 4 + 7 - 8 ) * 8'
   >>> solve(list('3322'))
   Solution found: ( 2 + 2 * 3 ) * 3
   '( 2 + 2 * 3 ) * 3'
   >>> solve(list('1111'))
   No solution found for: 1 1 1 1
   '!'
   >>> solve(list('123456'))
   Solution found: 1 + 2 + 3 * ( 4 + 5 ) - 6
   '1 + 2 + 3 * ( 4 + 5 ) - 6'
   >>> """
   digilen = len(digits)
   # length of an exp without brackets 
   exprlen = 2 * digilen - 1
   # permute all the digits
   digiperm = sorted(set(permutations(digits)))
   # All the possible operator combinations
   opcomb   = list(product('+-*/', repeat=digilen-1))
   # All the bracket insertion points:
   brackets = [()] + [(x,y)
                        for x in range(0, exprlen, 2)
                        for y in range(x+4, exprlen+2, 2)
                        if (x,y) != (0,exprlen+1)]
   for d in digiperm:
       for ops in opcomb:
           ex = list(chain(*zip_longest(d, ops, fillvalue=)))
           for b in brackets:
               exp = ex[::]
               if b:
                   exp.insert(b[0], '(')
                   exp.insert(b[1], ')')
               txt = .join(exp)
               try:
                   num = eval(txt)
               except ZeroDivisionError:
                   continue
               if num == 24:
                   ans = ' '.join(exp).rstrip()
                   print ("Solution found:",ans)
                   return ans
   print ("No solution found for:", ' '.join(digits))            
   return '!'

def main():

   digits = choose4()
   welcome(digits)
   trial = 0
   answer = 
   chk = ans = False
   while not (chk and ans == 24):
       trial +=1
       answer = input("Expression %i: " % trial)
       chk = check(answer, digits)
       if answer.lower() == '?':
           answer = solve(digits)
           break
       if answer.lower() == 'q':
           break
       if answer.lower() == '!':
           digits = choose4()
           print ("New digits:", ' '.join(digits))
           continue
       if not chk:
           print ("The input '%s' was wonky!" % answer)
       else:
           ans = eval(answer)
           print (" = ", ans)
           if ans == 24:
               print ("Thats right!")
   print ("Thank you and goodbye")

main()</lang>

Sample Output

 The 24 Game Player

 Given any four digits in the range 1 to 9, which may have repetitions,
 Using just the +, -, *, and / operators; and the possible use of
 brackets, (), show how to make an answer of 24.

 An answer of "q" will quit the game.
 An answer of "!" will generate a new set of four digits.
 An answer of "?" will compute an expression for the current digits.
 
 Otherwise you are repeatedly asked for an expression until it evaluates to 24

 Note: you cannot form multiple digit numbers from the supplied digits,
 so an answer of 12+12 when given 1, 2, 2, and 1 would not be allowed.


Your four digits: 6 7 9 5
Expression 1: ?
Solution found: 6 - ( 5 - 7 ) * 9
Thank you and goodbye