41 lines
1.2 KiB
C#
41 lines
1.2 KiB
C#
using System;
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using System.Collections.Generic;
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using System.Linq;
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namespace AdventOfCode.Extensions;
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public static class EnumerableExtensions
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{
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public static IEnumerable<TValue[]> Combinations<TValue>(this IEnumerable<TValue> values, int count)
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{
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var pool = values.ToArray();
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var poolLength = pool.Length;
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if (count > poolLength)
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yield break;
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var indices = Enumerable.Range(0, count).ToArray();
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yield return GetCombination(indices, pool);
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while (true)
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{
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int idx;
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for(idx = count - 1; idx >= 0; idx--)
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{
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var isIndexBelowMax = indices[idx] != idx + poolLength - count;
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if (isIndexBelowMax)
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break;
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}
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if(idx < 0)
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yield break;
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indices[idx] += 1;
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for (var j = idx + 1; j < count; j++)
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{
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indices[j] = indices[j - 1] + 1;
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}
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yield return GetCombination(indices, pool);
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}
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static TValue[] GetCombination(int[] innerIndices, TValue[] innerPool) =>
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innerIndices.Select(i => innerPool[i]).ToArray();
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}
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} |