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Add CombinationsWithRepeats method to EnumerableExtensions with corresponding tests

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This commit is contained in:
Sebastian Lindemeier
2025-12-15 13:45:21 +01:00
parent 149977d02f
commit 0665713725
2 changed files with 67 additions and 5 deletions
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AdventOfCode.Extensions/EnumerableExtensions.cs
+35 -3
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@@ -12,14 +12,15 @@ public static class EnumerableExtensions
var poolLength = pool.Length;
if (count > poolLength)
yield break;
var indices = Enumerable.Range(0, count).ToArray();
int[] indices = [..Enumerable.Range(0, count)];
yield return GetCombination(indices, pool);
while (true)
{
var idx = count - 1;
for(;idx >= 0; --idx)
{
var isIndexBelowMax = indices[idx] != idx + poolLength - count;
var maxPossibleIndex = idx + poolLength - count;
var isIndexBelowMax = indices[idx] != maxPossibleIndex;
if (isIndexBelowMax)
break;
}
@@ -27,7 +28,7 @@ public static class EnumerableExtensions
yield break;
indices[idx] += 1;
for (var j = idx + 1; j < count; j++)
for (var j = idx + 1; j < indices.Length; j++)
{
indices[j] = indices[j - 1] + 1;
}
@@ -36,6 +37,37 @@ public static class EnumerableExtensions
}
}
public static IEnumerable<TValue[]> CombinationsWithRepeats<TValue>(this IEnumerable<TValue> values, int count)
{
var pool = values.ToArray();
var poolLength = pool.Length;
if (count > poolLength)
yield break;
int[] indices = [..Enumerable.Repeat(0, count)];
yield return GetCombination(indices, pool);
while (true)
{
var idx = count - 1;
for(;idx >= 0; --idx)
{
var maxPossibleIndex = poolLength - 1;
var isIndexBelowMax = indices[idx] != maxPossibleIndex;
if (isIndexBelowMax)
break;
}
if(idx < 0)
yield break;
var num = indices[idx];
for (var j = idx; j < indices.Length; j++)
{
indices[j] = num + 1;
}
yield return GetCombination(indices, pool);
}
}
public static IEnumerable<TValue[]> Permutations<TValue>(this IEnumerable<TValue> values, int count)
{
var pool = values.ToArray();