Once you solve a problem, you can see other solutions of the same size or larger. You won't be able to see smaller solutions until you solve another problem in the same category. If that is not what is happening, then give us the list of problems you have solved and I'll ask the cody people to look at it.
Indeed there is not currently any way to see the solution to a problem you haven't solved. But any solution, even if not very good will allow you to unlock all the solutions (once you solve another problem).