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Improve Util.Shuffle.

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Reduce algorithmic complexity from O(n^2) to O(n).
This commit is contained in:
RoosterDragon
2016-02-13 22:19:46 +00:00
parent 2debda926a
commit 3a99111a42
1 changed files with 11 additions and 6 deletions
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17
OpenRA.Mods.Common/Util.cs
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@@ -77,16 +77,21 @@ namespace OpenRA.Mods.Common
return WPos.Lerp(w.Map.CenterOfCell(from), w.Map.CenterOfCell(to), 1, 2); return WPos.Lerp(w.Map.CenterOfCell(from), w.Map.CenterOfCell(to), 1, 2);
} }
/* pretty crap */
public static IEnumerable<T> Shuffle<T>(this IEnumerable<T> ts, MersenneTwister random) public static IEnumerable<T> Shuffle<T>(this IEnumerable<T> ts, MersenneTwister random)
{ {
var items = ts.ToList(); // Fisher-Yates
while (items.Count > 0) var items = ts.ToArray();
for (var i = 0; i < items.Length - 1; i++)
{ {
var t = items.Random(random); var j = random.Next(items.Length - i);
yield return t; var item = items[i + j];
items.Remove(t); items[i + j] = items[i];
items[i] = item;
yield return item;
} }
if (items.Length > 0)
yield return items[items.Length - 1];
} }
static IEnumerable<CPos> Neighbours(CPos c, bool allowDiagonal) static IEnumerable<CPos> Neighbours(CPos c, bool allowDiagonal)