From 9b8209f50ae27d756765ed03a545a0cec720a51e Mon Sep 17 00:00:00 2001
From: "google-labs-jules[bot]"
 <161369871+google-labs-jules[bot]@users.noreply.github.com>
Date: Fri, 21 Aug 2026 12:16:12 +0000
Subject: [PATCH] perf(CollectionExtensions): optimize WeightedRandom to avoid
 array allocation

Co-authored-by: johnstrand <11484777+johnstrand@users.noreply.github.com>
---
 .../Extensions/CollectionExtensions.cs        | 41 +++++++++----------
 1 file changed, 19 insertions(+), 22 deletions(-)

diff --git a/src/GameUtils/Extensions/CollectionExtensions.cs b/src/GameUtils/Extensions/CollectionExtensions.cs
index bc27b99..e1efe78 100644
--- a/src/GameUtils/Extensions/CollectionExtensions.cs
+++ b/src/GameUtils/Extensions/CollectionExtensions.cs
@@ -245,37 +245,34 @@ public static T WeightedRandom<T>(this IEnumerable<T> source, Func<T, float> wei
             return list[count - 1];
         }
 
-        var array = source.ToArray();
-        int arrayCount = array.Length;
-        if (arrayCount == 0)
-        {
-            throw new InvalidOperationException("Sequence contains no elements.");
-        }
+        T selected = default!;
+        float fallbackTotalWeight = 0f;
+        bool hasElements = false;
 
-        var arrayTotalWeight = 0f;
-        for (int i = 0; i < arrayCount; i++)
+        foreach (var item in source)
         {
-            arrayTotalWeight += weightSelector(array[i]);
+            hasElements = true;
+            float weight = weightSelector(item);
+            if (weight <= 0f) continue;
+
+            fallbackTotalWeight += weight;
+
+            if (Random.Shared.NextDouble() * fallbackTotalWeight < weight)
+            {
+                selected = item;
+            }
         }
 
-        if (arrayTotalWeight <= 0)
+        if (!hasElements)
         {
-            throw new InvalidOperationException("Total weight must be greater than zero.");
+            throw new InvalidOperationException("Sequence contains no elements.");
         }
 
-        var arrayTarget = (float)(Random.Shared.NextDouble() * arrayTotalWeight);
-        var arrayCumulative = 0f;
-
-        for (int i = 0; i < arrayCount; i++)
+        if (fallbackTotalWeight <= 0f)
         {
-            var item = array[i];
-            arrayCumulative += weightSelector(item);
-            if (arrayTarget <= arrayCumulative)
-            {
-                return item;
-            }
+            throw new InvalidOperationException("Total weight must be greater than zero.");
         }
 
-        return array[arrayCount - 1];
+        return selected;
     }
 }