Day 8

This one felt good. And I hit a new personal best on the global leaderboard of 562/404.

src/08.cs

@@ -0,0 +1,72 @@
+using Math = aoc2023.Util.Math;
+
+namespace aoc2023;
+
+internal class Day08 : Day
+{
+    private string directions = "";
+    private readonly Dictionary<string, (string left, string right)> nodes = [];
+    internal override void Parse()
+    {
+        var lines = Util.Parsing.ReadAllLines($"{GetDay()}").ToList();
+        directions = lines[0];
+        foreach (var line in lines.Skip(2))
+        {
+            var split = line.Split(" = ");
+            var choices = split[1].Trim('(', ')').Split(", ");
+            nodes.Add(split[0], (choices[0], choices[1]));
+        }
+    }
+
+    internal override string Part1()
+    {
+        var currNode = "AAA";
+        int i;
+        for (i = 0; currNode != "ZZZ"; i++)
+        {
+            if (directions[i % directions.Length] == 'R')
+            {
+                currNode = nodes[currNode].right;
+            }
+            else
+            {
+                currNode = nodes[currNode].left;
+            }
+        }
+
+        return $"Steps from AAA to ZZZ: <+white>{i}";
+    }
+
+    internal override string Part2()
+    {
+        List<string> currNodes = [];
+        foreach (var node in nodes)
+        {
+            if (node.Key.EndsWith('A'))
+            {
+                currNodes.Add(node.Key);
+            }
+        }
+
+        List<long> dists = [];
+        for (int n = 0; n < currNodes.Count; n++)
+        {
+            long i;
+            for (i = 0; !currNodes[n].EndsWith('Z'); i++)
+            {
+                if (directions[(int)(i % directions.Length)] == 'R')
+                {
+                    currNodes[n] = nodes[currNodes[n]].right;
+                }
+                else
+                {
+                    currNodes[n] = nodes[currNodes[n]].left;
+                }
+            }
+            dists.Add(i);
+        }
+
+        long totalDist = Math.LCM([.. dists]);
+        return $"Steps before all nodes ending in A are simultaneously on a node ending in Z: <+white>{totalDist}";
+    }
+}

src/Util/Math.cs

@@ -1,12 +1,14 @@
-namespace aoc2023.Util;
+using System.Numerics;
+
+namespace aoc2023.Util;
 
 public static class Math
 {
-    public static ulong GCD(ulong a, ulong b)
+    public static T GCD<T>(T a, T b) where T : IBinaryInteger<T>
     {
         while (true)
         {
-            if (b == 0)
+            if (b == T.Zero)
             {
                 return a;
             }
@@ -17,13 +19,13 @@ public static class Math
         }
     }
 
-    public static ulong LCM(params ulong[] nums)
+    public static T LCM<T>(params T[] nums) where T : IBinaryInteger<T>
     {
         var num = nums.Length;
         switch (num)
         {
             case 0:
-                return 0;
+                return T.Zero;
             case 1:
                 return nums[0];
         }
@@ -37,7 +39,7 @@ public static class Math
         return ret;
     }
 
-    private static ulong lcm(ulong a, ulong b)
+    private static T lcm<T>(T a, T b) where T : IBinaryInteger<T>
     {
         return (a * b) / GCD(a, b);
     }