how to calculate 24?

Question

I wrote a python script trying to solve the 'calculate 24' problem, which originated from a game, drawing 4 cards from a deck of cards and try to get the value 24 using +,-, *, and /.

The code is working, only that it have many duplications, for example, I input 2, 3, 4, 5 to get the value of 24, it will find and print that 2*(3 + 4 + 5) is 24, but it will also print 2*(5 + 4 + 3), 2*(5 + 3 + 4), etc., while it will find 4*(3 + 5 - 2), it will also print 4*(5 + 3 - 2). Could anyone please give me some hints on how to remove duplicated answers?

The code is as follows:

def calc(oprands, result) :
    ret=[]
    if len(oprands)==1 :
        if oprands[0]!=result :
            return ret
        else :
            ret.append(str(oprands[0]))
            return ret
    for idx, x in enumerate(oprands) :
        if x in oprands[0:idx] :
            continue
        remaining=oprands[0:idx]+oprands[idx+1:]
        temp = calc(remaining, result-x)         # try addition
        for s in temp :
            ret.append(str(x) + ' + ' + s)
        if(result%x == 0) :                      # try multiplication
            temp = calc(remaining, result/x)
            for s in temp :
                ret.append(str(x) + ' * (' + s + ')')
        temp = calc(remaining, result+x)          # try subtraction
        for s in temp :
            ret.append(s + ' - ' + str(x))
        temp = calc(remaining, x-result)
        for s in temp :
            ret.append(str(x) + ' - (' + s + ')')
        temp = calc(remaining, result*x)          # try division
        for s in temp :
            ret.append('(' + s + ') / ' + str(x))
        if result!=0 and x%result==0 and x/result!=0 :
            temp = calc(remaining, x/result)
            for s in temp :
                ret.append(str(x) + ' / ' + '(' +s +')')
    return ret

if __name__ == '__main__' :
    nums = raw_input("Please input numbers seperated by space: ")
    rslt = int(raw_input("Please input result: "))
    oprds = map(int, nums.split(' '))
    rr = calc(oprds, rslt)
    for s in rr :
        print s
    print 'calculate {0} from {1}, there are altogether {2} solutions.'.format(rslt, oprds, len(rr))

Answer 1

Calculate 24 is an interesting and challenging game. As other users pointed out in the comments, it's difficult to create a solution that doesn't present any flaw.

You could study the Rosetta Code (spoiler alert) implementation and compare it to your solution.