diff --git a/MatchingEngine.CLI/MatchingEngine.CLI.csproj b/MatchingEngine.CLI/MatchingEngine.CLI.csproj
index d7a9247..80d0eb0 100644
--- a/MatchingEngine.CLI/MatchingEngine.CLI.csproj
+++ b/MatchingEngine.CLI/MatchingEngine.CLI.csproj
@@ -1,6 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
     <PropertyGroup>
+        <Version>0.4.0</Version>
         <OutputType>Exe</OutputType>
         <TargetFramework>net7.0</TargetFramework>
         <AssemblyName>matching</AssemblyName>
diff --git a/MatchingEngine.Domain/Duplicate.cs b/MatchingEngine.Domain/Duplicate.cs
index e7437a3..4aab14f 100644
--- a/MatchingEngine.Domain/Duplicate.cs
+++ b/MatchingEngine.Domain/Duplicate.cs
@@ -1,5 +1,4 @@
 using System.Collections.Concurrent;
-using MatchingEngine.Domain.Helpers;
 using MatchingEngine.Domain.Models;
 
 namespace MatchingEngine.Domain;
@@ -37,55 +36,53 @@ private static Dictionary<char, int[]> GetCharactersStartAndEndIndex(ReadOnlySpa
         return characterIndex;
     }
 
-    public static ConcurrentBag<PotentialDuplicate> GetPotentialDuplicates(PatientRecord[] records1,
-        PatientRecord[] records2, double lowerScoreThreshold, double upperScoreThreshold)
+    public static ConcurrentBag<PotentialDuplicate> GetPotentialDuplicates(Memory<PatientRecord> records1,
+        Memory<PatientRecord> records2, double lowerScoreThreshold, double upperScoreThreshold)
     {
-        var characterStartAndEndIndex = GetCharactersStartAndEndIndex(records2);
         var potentialDuplicates = new ConcurrentBag<PotentialDuplicate>();
-        Parallel.For(0, records1.Length,
-            primaryRecordIndex =>
-            {
-                CompareRecords(potentialDuplicates, primaryRecordIndex, records1, records2, characterStartAndEndIndex,
-                    lowerScoreThreshold, upperScoreThreshold);
-            });
-        return potentialDuplicates;
-    }
 
-    private static void CompareRecords(ConcurrentBag<PotentialDuplicate> potentialDuplicates, int primaryIndex,
-        ReadOnlySpan<PatientRecord> primaryRecords, PatientRecord[] recordsToCompare,
-        IReadOnlyDictionary<char, int[]> characterStartAndEndIndex, double lowerScoreThreshold,
-        double upperScoreThreshold)
-    {
-        var primaryRecord = primaryRecords[primaryIndex];
-        int[]? indices = null;
-        _ = primaryRecord.FirstName.Length > 0 &&
-            characterStartAndEndIndex.TryGetValue(primaryRecord.FirstName[0], out indices);
-        
-        var start = indices != null ? indices[0] : 0;
-        var end = indices != null ? indices[1] : recordsToCompare.Length;
+        var records1CharacterStartAndEndIndex = GetCharactersStartAndEndIndex(records1.Span);
+        var records2CharacterStartAndEndIndex = GetCharactersStartAndEndIndex(records2.Span);
+
+        Parallel.ForEach(records1CharacterStartAndEndIndex, record1StartAndEnd =>
+        {
+            var records2StartAndEndFound =
+                records2CharacterStartAndEndIndex.TryGetValue(record1StartAndEnd.Key, out var records2StartAndEnd);
 
-        Parallel.For(start, end, list2Index =>
+            var records1ToCompare = records1.Slice(record1StartAndEnd.Value[0],
+                record1StartAndEnd.Value[1] - record1StartAndEnd.Value[0]);
+
+            var records2ToCompare = records2StartAndEndFound && records2StartAndEnd != null
+                ? records2.Slice(records2StartAndEnd[0], records2StartAndEnd[1] - records2StartAndEnd[0])
+                : records2;
+
+            Parallel.For(0, records1ToCompare.Length, recordToCompareIndex =>
             {
-                CompareRecordsInnerLoop(potentialDuplicates, primaryRecord, list2Index, recordsToCompare,
-                    lowerScoreThreshold, upperScoreThreshold);
+                var primaryRecord = records1ToCompare.Span[recordToCompareIndex];
+                for (var i = 0; i < records2ToCompare.Length; i++)
+                {
+                    var secondaryRecord = records2ToCompare.Span[i];
+                    CompareRecords(potentialDuplicates, ref primaryRecord, ref secondaryRecord,
+                        lowerScoreThreshold, upperScoreThreshold);
+                }
             });
+        });
+
+        return potentialDuplicates;
     }
 
-    private static void CompareRecordsInnerLoop(ConcurrentBag<PotentialDuplicate> potentialDuplicates,
-        PatientRecord primaryRecord, int recordToCompareIndex, ReadOnlySpan<PatientRecord> recordsToCompare,
+    private static void CompareRecords(ConcurrentBag<PotentialDuplicate> potentialDuplicates,
+        ref PatientRecord primaryRecord, ref PatientRecord secondaryRecord,
         double lowerScoreThreshold, double upperScoreThreshold)
     {
-        var tempRecord = recordsToCompare[recordToCompareIndex];
-        //check if the first character of the first name is equal
-        if (!StringHelpers.FirstCharactersAreEqual(primaryRecord.FirstName, tempRecord.FirstName) ||
-            primaryRecord.RecordId == tempRecord.RecordId) return;
+        if (primaryRecord.RecordId == secondaryRecord.RecordId) return;
         //get the distance vector for the ith vector of the first table and the jth record of the second table
-        var distanceVector = DistanceVector.CalculateDistance(primaryRecord, tempRecord);
+        var distanceVector = DistanceVector.CalculateDistance(ref primaryRecord, ref secondaryRecord);
         var tempScore = Score.CalculateFinalScore(ref distanceVector);
         if (tempScore >= lowerScoreThreshold && tempScore <= upperScoreThreshold)
         {
             potentialDuplicates.Add(
-                new PotentialDuplicate(primaryRecord, tempRecord, distanceVector, tempScore));
+                new PotentialDuplicate(primaryRecord, secondaryRecord, distanceVector, tempScore));
         }
     }
 }
\ No newline at end of file
diff --git a/MatchingEngine.Domain/Models/DistanceVector.cs b/MatchingEngine.Domain/Models/DistanceVector.cs
index 27a0c7b..55b46b5 100644
--- a/MatchingEngine.Domain/Models/DistanceVector.cs
+++ b/MatchingEngine.Domain/Models/DistanceVector.cs
@@ -10,7 +10,7 @@ public readonly record struct DistanceVector
     public int CityDistance { get; private init; }
     public int PhoneNumberDistance { get; private init; }
 
-    public static DistanceVector CalculateDistance(PatientRecord firstRecord, PatientRecord secondRecord)
+    public static DistanceVector CalculateDistance(ref PatientRecord firstRecord, ref PatientRecord secondRecord)
     {
         return new DistanceVector
         {
diff --git a/MatchingEngine.Domain/Models/PatientRecord.cs b/MatchingEngine.Domain/Models/PatientRecord.cs
index 3804297..f931c71 100644
--- a/MatchingEngine.Domain/Models/PatientRecord.cs
+++ b/MatchingEngine.Domain/Models/PatientRecord.cs
@@ -1,6 +1,6 @@
 namespace MatchingEngine.Domain.Models;
 
-public sealed record PatientRecord
+public readonly record struct PatientRecord
 (
     string RecordId,
     string FirstName,