12/12/2023 0 Comments Permutation algorithm![]() ![]() Or if this is to difficult, stop using iterator blocks and let the recursive method take a list that it adds results to. ![]() This probably means that you need to keep track of an explicit stack of the numbers to process. The second change I would try would be to try rewrite the recursion to an iterative implementation. That way you can tell if any changes actually improves the situation or not. The first thing you should do is add code to measure the performance, or even better, use a profiler. It is a benefit if you concatenate many strings, but as far as I can see you only add two strings together. This is quite inefficient.Ī can also not see that stringBuilder gives any advantage here. ![]() MoveNext() method is will advance one step of the loop, that will call MoveNext() in turn etc, resulting in N calls to MoveNext(), new StringBuilder, Append() etc. Permutations is a recursive function that implements an iterator. We can understand how it work as follows: Put the nth element in all positions. It adds lexicographic ordering to figure out how to generate permutations and change direction. If you want to know how this works, read Eric Lipper's excellent article, which I linked above.Ĭonsider foreach (var result in Permutations(n + 1, k + 1)) The algorithm derives from Basic Permutation 2: Insert and is, in essence, the same as the minimal change version we saw earlier. Source = "0123456789abcdefghijklmnopqr".ToCharArray() You can extend this to 28 characters by modifying the source data: source = "0123456789abcdefghijklmnopqr".ToCharArray() Public static IEnumerable> Combine(IEnumerable> sequences) We can apply this to your problem like so: using System What you're outputting there is the cartesian product of two sets the first set is the characters "0123456789ab" and the second set is the characters "123456789ab".Įric Lippert wrote a well-known article demonstrating how to use Linq to solve this. Yield return new StringBuilder().Append(element).Append(result) įoreach (var element in new PermutationGenerator(2)) Private IEnumerable Permutations(int n, int k)įoreach (var result in Permutations(n + 1, k + 1)) Public class PermutationGenerator : IEnumerable below is the current code I am looking to optimize. if I can have this converted into a for loop with 28 characters of alphanumeric, that would be awesome. I have this permutation code working perfectly but it does not generate the code fast enough, I need help with optimizing the code to run faster, please it is important that the result remains the same, I have seen other algorithms but they don't into consideration the output length and same character reputation which are all valid output. ![]()
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