I’ve been trying to calculate all the unique permutations for a very long word (antidisestablishmentarianism), and although I can calculate the permutations for the words, I am having problems with stopping the production of duplications.
Normally I would just run the List<T>.Contains() method on my string, but the list of permutations becomes so large I can’t keep it in memory. I made that mistake earlier and managed to use up all 8GB of memory in my computer. In order to prevent that from happening again, I changed the code to append the calculated permutation to a file and release it from memory.
My main question is this: How can I prevent duplicate permutations from being added to my file without loading the whole thing in memory? Is it possible to selectively load, for example, the first few megabytes, scan that, and move on until the file is completed, or should I be looking in a different direction?
This is not homework, my math homework gave a hypothetical situation where a computer could calculate 30 permutations per second and made me figure out how long it would take to calculate all the permutations. That wasn’t a problem, and I don’t need help with that, I just wanted to know how long it would take a modern computer to perform the same task.
How about using an algorithm that generates all permutations without duplicates? That way you wouldn’t have to check for them in the first place.
A Google search for ‘algorithm generate permutations’ turns up dozens of references to get you started. e.g. Permutation Generation Methods