[Core] Fix issues with sorting/grouping in MultiValueSortedList

Author: Kryptos-FR

sources/core/Stride.Core.Tests/Collections/MultiValueSortedListTests.cs

@@ -24,21 +24,23 @@ public void Add_SingleValue_AddsToList()
         Assert.Single(list);
     }
 
-    [Fact(Skip = "Implementation has issues with retrieving all values for a key")]
+    [Fact]
     public void Add_MultipleValuesWithSameKey_AllAdded()
     {
         var list = new MultiValueSortedList<int, string>();
         list.Add(new KeyValuePair<int, string>(1, "first"));
         list.Add(new KeyValuePair<int, string>(1, "second"));
         list.Add(new KeyValuePair<int, string>(1, "third"));
 
-        // All 3 values are properly added
         Assert.Equal(3, list.Count);
         var values = list[1].ToList();
-        Assert.Single(values);
+        Assert.Equal(3, values.Count);
+        Assert.Contains("first", values);
+        Assert.Contains("second", values);
+        Assert.Contains("third", values);
     }
 
-    [Fact(Skip = "Implementation has sorting issues")]
+    [Fact]
     public void Add_MaintainsSortedOrder()
     {
         var list = new MultiValueSortedList<int, string>();
@@ -62,8 +64,9 @@ public void Indexer_ReturnsValuesForKey()
         var valuesFor1 = list[1].ToList();
         var valuesFor2 = list[2].ToList();
 
-        // Note: Implementation has an issue with multiple values per key
-        Assert.Single(valuesFor1);
+        Assert.Equal(2, valuesFor1.Count);
+        Assert.Contains("a", valuesFor1);
+        Assert.Contains("b", valuesFor1);
         Assert.Single(valuesFor2);
         Assert.Contains("c", valuesFor2);
     }
@@ -142,7 +145,7 @@ public void Remove_NonExistentKey_ReturnsFalse()
         Assert.Single(list);
     }
 
-    [Fact(Skip = "Implementation has sorting issues")]
+    [Fact]
     public void Keys_ReturnsDistinctKeysInOrder()
     {
         var list = new MultiValueSortedList<int, string>();
@@ -172,7 +175,7 @@ public void Values_ReturnsAllValues()
         Assert.Contains("c", values);
     }
 
-    [Fact(Skip = "Implementation has grouping issues")]
+    [Fact]
     public void GetEnumerator_GroupsByKey()
     {
         var list = new MultiValueSortedList<int, string>();
@@ -227,7 +230,7 @@ public void CopyTo_CopiesAllElements()
         Assert.NotEqual(default, array[2]);
     }
 
-    [Fact(Skip = "Implementation has sorting issues")]
+    [Fact]
     public void MixedKeys_MaintainsSortOrder()
     {
         var list = new MultiValueSortedList<int, string>();

sources/core/Stride.Core/Collections/MultiValueSortedList.cs

@@ -83,23 +83,25 @@ IEnumerator IEnumerable.GetEnumerator()
 
     public void Add(KeyValuePair<TKey, TValue> item)
     {
+        // Binary search to find insertion point
         var lower = 0;
-        var greater = list.Count;
-        var current = (lower + greater) >> 1;
-        while (greater - lower > 1)
+        var upper = list.Count;
+        
+        while (lower < upper)
         {
-            if (keys[current].CompareTo(item.Key) < 0)
+            var mid = lower + (upper - lower) / 2;
+            if (keys[mid].CompareTo(item.Key) < 0)
             {
-                lower = current;
+                lower = mid + 1;
             }
             else
             {
-                greater = current;
+                upper = mid;
             }
-            current = (lower + greater) >> 1;
         }
-        list.Insert(greater, item);
-        keys.Insert(greater, item.Key);
+        
+        list.Insert(lower, item);
+        keys.Insert(lower, item.Key);
     }
 
     public bool Contains(object key)
@@ -152,7 +154,22 @@ public bool Contains(TKey key)
 
     public int Count => list.Count;
 
-    public IEnumerable<TValue> this[TKey key] { get { return list.Skip(KeyToIndex(key)).TakeWhile(x => x.Key.Equals(key)).Select(x => x.Value); } }
+    public IEnumerable<TValue> this[TKey key]
+    {
+        get
+        {
+            var index = KeyToIndex(key);
+            if (index < 0) return Enumerable.Empty<TValue>();
+            
+            // Binary search may return any matching index, so we need to find the first one
+            while (index > 0 && keys[index - 1].Equals(key))
+            {
+                index--;
+            }
+            
+            return list.Skip(index).TakeWhile(x => x.Key.Equals(key)).Select(x => x.Value);
+        }
+    }
 
     int ICollection.Count => list.Count;