Created
October 18, 2023 18:42
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Combinatorics
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| namespace Scripts; | |
| public class Combinatorics | |
| { | |
| public static IEnumerable<IEnumerable<T>> GetPermutations<T>(List<T> input, int i = 0) | |
| { | |
| if (i >= input.Count - 1) | |
| { | |
| yield return input.ToList(); | |
| } | |
| else | |
| { | |
| foreach (var permutation in GetPermutations(input, i + 1)) | |
| { | |
| yield return permutation; | |
| } | |
| for (int j = i + 1; j < input.Count; ++j) | |
| { | |
| (input[i], input[j]) = (input[j], input[i]); | |
| foreach (var permutation in GetPermutations(input, i + 1)) | |
| { | |
| yield return permutation; | |
| } | |
| (input[i], input[j]) = (input[j], input[i]); | |
| } | |
| } | |
| } | |
| public static IEnumerable<IEnumerable<T>> GetCombinations<T>(List<T> input, int count = 0) | |
| { | |
| List<T> buffer = new(count); | |
| foreach (var combination in GetCombinations(input, buffer, 0, count)) | |
| { | |
| yield return combination; | |
| } | |
| } | |
| private static IEnumerable<IEnumerable<T>> GetCombinations<T>(List<T> input, List<T> buffer, int offset, int count) | |
| { | |
| if (count == 0) | |
| { | |
| yield return buffer.ToList(); | |
| } | |
| else | |
| { | |
| for (int i = offset; i <= input.Count - count; ++i) | |
| { | |
| buffer.Add(input[i]); | |
| foreach (var combination in GetCombinations(input, buffer, i + 1, count - 1)) | |
| { | |
| yield return combination; | |
| } | |
| buffer.RemoveAt(buffer.Count - 1); | |
| } | |
| } | |
| } | |
| } |
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