From bef54ff55100d7c7860dbc35e98704383f56d76d Mon Sep 17 00:00:00 2001
From: Sebastian Lindemeier <lindemeier.sebastian@bgetem.de>
Date: Fri, 12 Dec 2025 20:37:31 +0100
Subject: [PATCH] Introduce regex-based methods `SolvePart1Regex` and
 `SolvePart2Regex` in Day02 for another invalid ID detection

---
 AoC_2025.Tests/Day02Test.cs | 32 +++++++++++++++++++++++++++
 AoC_2025/Day02.cs           | 44 +++++++++++++++++++++++++++++++++++--
 2 files changed, 74 insertions(+), 2 deletions(-)

diff --git a/AoC_2025.Tests/Day02Test.cs b/AoC_2025.Tests/Day02Test.cs
index fce2908..85fb9ff 100644
--- a/AoC_2025.Tests/Day02Test.cs
+++ b/AoC_2025.Tests/Day02Test.cs
@@ -29,6 +29,22 @@ public class Day02Test
         Assert.Equal(13919717792, actual);
     }
     
+    [Fact]
+    public void Part01Regex_Test_equals_4174379265()
+    {
+        var actual = (_sut as Day02).SolvePart1Regex(TestInputPath);
+        
+        Assert.Equal(1227775554, actual);
+    }
+    
+    [Fact]
+    public void Part01Regex_Prod_equals_14582313461()
+    {
+        var actual = (_sut as Day02).SolvePart1Regex(ProdInputPath);
+        
+        Assert.Equal(13919717792, actual);
+    }
+    
     [Fact]
     public void Part02_Test_equals_4174379265()
     {
@@ -44,4 +60,20 @@ public class Day02Test
         
         Assert.Equal(14582313461, actual);
     }
+    
+    [Fact]
+    public void Part02Regex_Test_equals_4174379265()
+    {
+        var actual = (_sut as Day02).SolvePart2Regex(TestInputPath);
+        
+        Assert.Equal(4174379265, actual);
+    }
+    
+    [Fact]
+    public void Part02Regex_Prod_equals_14582313461()
+    {
+        var actual = (_sut as Day02).SolvePart2Regex(ProdInputPath);
+        
+        Assert.Equal(14582313461, actual);
+    }
 }
\ No newline at end of file
diff --git a/AoC_2025/Day02.cs b/AoC_2025/Day02.cs
index e08cb18..8bbea8a 100644
--- a/AoC_2025/Day02.cs
+++ b/AoC_2025/Day02.cs
@@ -1,8 +1,9 @@
-using AdvenOfCode.Contracts;
+using System.Text.RegularExpressions;
+using AdvenOfCode.Contracts;
 
 namespace AoC_2025;
 
-public class Day02 : IPuzzleSolver<long>
+public partial class Day02 : IPuzzleSolver<long>
 {
     private string[] ParsePuzzleInput(string path)
     {
@@ -20,6 +21,14 @@ public class Day02 : IPuzzleSolver<long>
         return sum;
     }
     
+    public long SolvePart1Regex(string pathToPuzzleInput)
+    {
+        var idRanges = ParsePuzzleInput(pathToPuzzleInput);
+        var invalidIds = idRanges.SelectMany(range => FindInvalidIdsRegex(range));
+        var sum = invalidIds.Sum();
+        return sum;
+    }
+    
     public long SolvePart2(string pathToPuzzleInput)
     {
         var idRanges = ParsePuzzleInput(pathToPuzzleInput);
@@ -27,6 +36,14 @@ public class Day02 : IPuzzleSolver<long>
         var sum = invalidIds.Sum();
         return sum;
     }
+    
+    public long SolvePart2Regex(string pathToPuzzleInput)
+    {
+        var idRanges = ParsePuzzleInput(pathToPuzzleInput);
+        var invalidIds = idRanges.SelectMany(range => FindInvalidSegmentedIdsRegex(range));
+        var sum = invalidIds.Sum();
+        return sum;
+    }
 
     private IEnumerable<long> FindInvalidIds(string range)
     {
@@ -36,6 +53,24 @@ public class Day02 : IPuzzleSolver<long>
         return invalidIds;
     }
     
+    private IEnumerable<long> FindInvalidIdsRegex(string range)
+    {
+        return FindAllInvalidIds(range, RepeatedInputRegex());
+    }
+    
+    private IEnumerable<long> FindInvalidSegmentedIdsRegex(string range)
+    {
+        return FindAllInvalidIds(range, SegmentRepeatedInputRegex());
+    }
+    
+    private IEnumerable<long> FindAllInvalidIds(string range, Regex regex)
+    {
+        var (start, end) = Parse(range);
+        var invalidIds = Range(start, end)
+            .Where(id => regex.IsMatch(id.ToString()));
+        return invalidIds;
+    }
+    
     private IEnumerable<long> FindInvalidSegmentedIds(string range)
     {
         var (start, end) = Parse(range);
@@ -128,4 +163,9 @@ public class Day02 : IPuzzleSolver<long>
             (tuple, segment) => (tuple.allEqual && (tuple.prev == "" || tuple.prev == segment), segment));
         return allEqual;
     }
+
+    [GeneratedRegex(@"^(.+)\1+$")]
+    private static partial Regex SegmentRepeatedInputRegex();
+    [GeneratedRegex(@"^(.+)\1$")]
+    private static partial Regex RepeatedInputRegex();
 }
\ No newline at end of file