Merging and Count

Added Merging functionality
Added Count property returning rounded number.

Author: MCUnderground

HLL.NET.Tests/HyperLogLogMergeTests.cs

@@ -0,0 +1,43 @@
+using HLL.NET.Hashing;
+using HLL.NET.Models;
+
+namespace HLL.NET.Tests
+{
+    public class HyperLogLogMergeTests
+    {
+        private readonly IHasher<string> _hasher = new StringHasher();
+
+        [Fact]
+        public void Merge_WithDifferentPrecisions_ShouldThrow()
+        {
+            var hll1 = new HyperLogLog<string>(12, _hasher);
+            var hll2 = new HyperLogLog<string>(14, _hasher);
+
+            Assert.Throws<InvalidOperationException>(() => hll1.Merge(hll2));
+        }
+
+        [Fact]
+        public void Merge_WithSamePrecision_ShouldCombineRegisters()
+        {
+            var hll1 = new HyperLogLog<string>(12, _hasher);
+            var hll2 = new HyperLogLog<string>(12, _hasher);
+
+            for (int i = 0; i < 500; i++)
+                hll1.Add($"userA_{i}");
+
+            for (int i = 0; i < 700; i++)
+                hll2.Add($"userB_{i}");
+
+            double estimate1 = hll1.Estimate();
+            double estimate2 = hll2.Estimate();
+
+            hll1.Merge(hll2);
+
+            double mergedEstimate = hll1.Estimate();
+
+            // Merged estimate should be at least as large as either individual estimate
+            Assert.True(mergedEstimate >= estimate1, $"Merged estimate {mergedEstimate} is less than estimate1 {estimate1}");
+            Assert.True(mergedEstimate >= estimate2, $"Merged estimate {mergedEstimate} is less than estimate2 {estimate2}");
+        }
+    }
+}

HLL.NET/HLL.NET.csproj

@@ -3,7 +3,7 @@
 	<PropertyGroup>
 		<TargetFramework>netstandard2.0</TargetFramework>
 		<PackageId>HLL.NET</PackageId>
-		<Version>1.0.4</Version>
+		<Version>1.0.5</Version>
 		<Authors>MCUnderground</Authors>
 		<Description>A simple and efficient C# implementation of HyperLogLog for approximate cardinality estimation.</Description>
 		<PackageLicenseExpression>MIT</PackageLicenseExpression>

HLL.NET/HyperLogLog.cs

@@ -45,6 +45,23 @@ public void Add(T item)
             _registers[index].Update((byte)leadingZeros);
         }
 
+        public void Merge(HyperLogLog<T> other)
+        {
+            if (other == null)
+                throw new ArgumentNullException(nameof(other));
+
+            if (Precision != other.Precision)
+                throw new InvalidOperationException("Cannot merge HyperLogLogs with different precisions.");
+
+            for (int i = 0; i < _numRegisters; i++)
+            {
+                _registers[i].Update(other._registers[i].Value);
+            }
+
+        }
+
+        public ulong Count => (ulong)Math.Round(Estimate());
+
         public double Estimate()
         {
             double alphaMM = GetAlphaMM();