Question

I came across a fun math problem yesterday and have it solved, but with the code I wrote, I had to do a keyboard interrupt or it would run forever, lol. So I changed it to have an end condition, but now it only prints 1 solution and stops.

The problem goes like this: “You have the numbers 123456789, in that order. Between each number, you must insert either nothing, a plus sign, or a multiplication sign, so that the resulting expression equals 2002. Write a program that prints all solutions. (There are two.)”

import random


def try1(param):
    global solved
    opers = ['+', '*', '']
    hotpotato = ('%s'.join(param) % (random.choice(opers),
                                     random.choice(opers),
                                     random.choice(opers),
                                     random.choice(opers),
                                     random.choice(opers),
                                     random.choice(opers),
                                     random.choice(opers),
                                     random.choice(opers),
                                     )
             )
    if eval(hotpotato) == 2002:
        solved += 1
        print "Solution:", hotpotato, "= 2002     :-)"

    else:
        pass


solved = 0
while solved == 0:
    try1('123456789')

This code prints the first solution it encounters and stops. Can anyone tell me how to get it to print both solutions before it stops?

Answer 1

Store your solutions in a set:

solutions = set([])

Each time a solution is found, update the set:

solutions.append(solution)

Sets are nice because there don’t store duplicates:

>>> len(set([1, 1, 1, 1, 1, 1, 1]))
1

So just loop until the set’s size is greater than one:

while len(solved) < 2:
    try1('123456789')

---

Also, you can shorten this code:

hotpotato = ('%s'.join(param) % (random.choice(opers),
                                 random.choice(opers),
                                 random.choice(opers),
                                 random.choice(opers),
                                 random.choice(opers),
                                 random.choice(opers),
                                 random.choice(opers),
                                 random.choice(opers),
                                 )
         )

To this:

hotpotato = ('%s'.join(param) % (random.choice(opers) for i in range(8))))