From ade1148cc060bb73ce7c0915bad7a4a1794dd6fe Mon Sep 17 00:00:00 2001
From: Ben Harris <ben@tilde.team>
Date: Fri, 11 Nov 2022 16:31:34 -0500
Subject: [PATCH] 2015 day 4

---
 AOC.Test/Test2015.cs        |  2 ++
 AOC2015/Day04.cs            | 35 ++++++++++++++++++++++++++++++++---
 AOC2015/input2015/test04.in |  1 +
 3 files changed, 35 insertions(+), 3 deletions(-)
 create mode 100644 AOC2015/input2015/test04.in

diff --git a/AOC.Test/Test2015.cs b/AOC.Test/Test2015.cs
index 28c2fe3..08adb01 100644
--- a/AOC.Test/Test2015.cs
+++ b/AOC.Test/Test2015.cs
@@ -9,6 +9,7 @@ public class Test2015
     [DataRow(typeof(Day01), "232", "1783")]
     [DataRow(typeof(Day02),"1586300", "3737498")]
     [DataRow(typeof(Day03), "2081", "2341")]
+    // [DataRow(typeof(Day04), "346386", "9958218")]
     public void TestAllDays(Type dayType, string part1, string part2)
     {
         Common.CheckDay(dayType, part1, part2);
@@ -18,6 +19,7 @@ public class Test2015
     [DataRow(typeof(Day01), "-1", "5")]
     [DataRow(typeof(Day02), "58", "34")]
     [DataRow(typeof(Day03), "2", "11")]
+    // [DataRow(typeof(Day04), "609043", "6742839")]
     public void CheckTestInputs(Type dayType, string part1, string part2)
     {
         Day.UseTestInput = true;
diff --git a/AOC2015/Day04.cs b/AOC2015/Day04.cs
index ad56125..2fa2cdd 100644
--- a/AOC2015/Day04.cs
+++ b/AOC2015/Day04.cs
@@ -1,15 +1,44 @@
-namespace AOC2015;
+using System.Security.Cryptography;
+
+namespace AOC2015;
 
 /// <summary>
 /// Day 4: <see href="https://adventofcode.com/2015/day/4"/>
 /// </summary>
 public sealed class Day04 : Day
 {
+    private readonly string _key;
+
     public Day04() : base(2015, 4, "Puzzle Name")
     {
+        _key = Input.First();
     }
 
-    public override object Part1() => "";
+    public override object Part1()
+    {
+        var md5 = MD5.Create();
+        var counter = 0;
 
-    public override object Part2() => "";
+        while (true)
+        {
+            var hash = md5.ComputeHash(Encoding.ASCII.GetBytes(_key + counter));
+            if (BitConverter.ToString(hash).Replace("-", "").StartsWith("00000")) 
+                return counter;
+            counter++;
+        }
+    }
+
+    public override object Part2()
+    {
+        var md5 = MD5.Create();
+        var counter = 0;
+
+        while (true)
+        {
+            var hash = md5.ComputeHash(Encoding.ASCII.GetBytes(_key + counter));
+            if (BitConverter.ToString(hash).Replace("-", "").StartsWith("000000"))
+                return counter;
+            counter++;
+        }
+    }
 }
diff --git a/AOC2015/input2015/test04.in b/AOC2015/input2015/test04.in
new file mode 100644
index 0000000..0373d93
--- /dev/null
+++ b/AOC2015/input2015/test04.in
@@ -0,0 +1 @@
+abcdef