[2k25] Add day 1

Days/Day1.cs

@@ -5,60 +5,83 @@ namespace AdventOfCode.Days;
 public class Day1 : Day
 {
     public override int Number => 1;
-    public override string Name => "Historian Hysteria";
+    public override string Name => "Secret Entrance";
 
     public override void RunPart1(bool display = true)
     {
-        List<int> leftNumbers = [];
-        List<int> rightNumbers = [];
+        var password = 0;
+        var dialPosition = 50;
 
-        foreach (var line in Input.AsSpan().EnumerateLines())
+        foreach (var line in Input.EnumerateLines())
         {
-            var separatorIndex = line.IndexOf(' ');
+            var direction = line[0];
+            var offset = int.Parse(line[1..]);
 
-            leftNumbers.Add(int.Parse(line[..separatorIndex]));
-            rightNumbers.Add(int.Parse(line[(separatorIndex + 1)..]));
+            var sign = direction is 'L'
+                ? -1
+                : +1;
+
+            dialPosition = MathMod(dialPosition + (offset * sign), 100);
+
+            if (dialPosition is 0)
+            {
+                password++;
+            }
         }
 
-        leftNumbers.Sort();
-        rightNumbers.Sort();
-
-        var totalDistance = leftNumbers.Zip(rightNumbers, (a, b) => Math.Abs(a - b)).Sum();
-
         if (display)
         {
-            AnsiConsole.MarkupLine($"[green]Total distance is: [yellow]{totalDistance}[/][/]");
+            AnsiConsole.MarkupLine($"[green]Safe password is: [yellow]{password}[/][/]");
         }
     }
 
     public override void RunPart2(bool display = true)
     {
-        List<int> leftNumbers = [];
-        Dictionary<int, int> rightNumbersCount = [];
-        var similarityScore = 0;
+        var password = 0;
+        var dialPosition = 50;
 
-        foreach (var line in Input.AsSpan().EnumerateLines())
+        foreach (var line in Input.EnumerateLines())
         {
-            var separatorIndex = line.IndexOf(' ');
+            var direction = line[0];
+            var offset = int.Parse(line[1..]);
 
-            leftNumbers.Add(int.Parse(line[..separatorIndex]));
+            var originalSign = Math.Sign(dialPosition);
 
-            var rightNumber = int.Parse(line[(separatorIndex + 1)..]);
+            var sign = direction is 'L'
+                ? -1
+                : +1;
 
-            if (!rightNumbersCount.TryAdd(rightNumber, 1))
+            dialPosition = dialPosition + (offset * sign);
+
+            int clickCount;
+            if (dialPosition is 0)
             {
-                rightNumbersCount[rightNumber]++;
+                clickCount = 1;
             }
-        }
+            else
+            {
+                clickCount = Math.Abs(dialPosition) / 100; // Number of times the dial passed by 0
 
-        foreach (var leftNumber in leftNumbers)
-        {
-            similarityScore += leftNumber * rightNumbersCount.GetValueOrDefault(leftNumber);
+                // If we did a loop around it counts as a "click" too
+                if (originalSign != 0 && originalSign != Math.Sign(dialPosition))
+                {
+                    clickCount++;
+                }
+            }
+
+            dialPosition = MathMod(dialPosition, 100);
+
+            password += clickCount;
         }
 
         if (display)
         {
-            AnsiConsole.MarkupLine($"[green]Similarity score is: [yellow]{similarityScore}[/][/]");
+            AnsiConsole.MarkupLine($"[green]Safe password is: [yellow]{password}[/][/]");
         }
     }
+
+    private static int MathMod(int left, int right)
+    {
+        return (Math.Abs(left * right) + left) % right;
+    }
 }