From bebd257ef7e119299e7e51ad929e18883822a11c Mon Sep 17 00:00:00 2001
From: Jake <jake@jakecharman.co.uk>
Date: Sat, 3 Dec 2022 15:40:06 +0000
Subject: [PATCH] Completed 2015 day 4

---
 2015/Day-04/Day04.cs | 57 ++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 57 insertions(+)
 create mode 100644 2015/Day-04/Day04.cs

diff --git a/2015/Day-04/Day04.cs b/2015/Day-04/Day04.cs
new file mode 100644
index 0000000..fff6c39
--- /dev/null
+++ b/2015/Day-04/Day04.cs
@@ -0,0 +1,57 @@
+using System.Security.Cryptography;
+using System.Text;
+
+// Placeholders for values that need to be updated by multiple threads.
+int nextNum;
+int theNumber;
+
+// Read the input into a string.
+string input = File.ReadAllText(@"input.txt").ToString();
+
+// Generate an MD5 from our input plus a number. Update the global var if MD5 matches goal.
+bool checkMD5(int num, string goal){
+    string currentMd5 = new string('x', goal.Count());
+    using (MD5 md5 = MD5.Create()){
+        byte[] hashBytes = md5.ComputeHash(Encoding.ASCII.GetBytes(input+num.ToString()));
+        var sBuilder = new StringBuilder();
+        for (int i = 0; i < hashBytes.Length; i++)
+        {
+            sBuilder.Append(hashBytes[i].ToString("x2"));
+        }
+        currentMd5 = sBuilder.ToString();
+    }
+    if(currentMd5.Substring(0,goal.Count()) == goal && theNumber == 0){
+        theNumber = num;
+        return true;
+    }
+    return false;
+}
+
+// Keep running checkMD5 incrementing the number it appends each time.
+void mine(string goal){
+    while(checkMD5(nextNum, goal) == false && theNumber == 0){
+        nextNum++;
+    }
+}
+
+// Start n threads all running the mine function for a given goal
+int startThreads(string goal, int numThreads){
+    theNumber = 0;
+    nextNum = 0;
+    for(int i = 0; i < numThreads; i++){
+        Thread thread = new Thread(() => mine(goal)){
+            Name = "thread" + "_" + goal + i.ToString()
+        };
+        thread.Start();
+    }
+    while(theNumber == 0){
+
+    }
+    return theNumber;
+}
+
+// Print the result.
+DateTime start = DateTime.Now;
+Console.WriteLine("Part 1: " + startThreads("00000", 4));
+Console.WriteLine("Part 2: " + startThreads("000000", 4));
+Console.WriteLine("Time taken: " + DateTime.Now.Subtract(start));