Day 9

AoC2018.Runner/AoC2018.Runner.csproj

@@ -28,6 +28,9 @@
     <None Update="Input\day04.txt">
       <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
     </None>
+    <None Update="Input\day09.txt">
+      <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
+    </None>
     <None Update="Input\day08.txt">
       <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
     </None>

AoC2018.Runner/Input/day09.txt

@@ -0,0 +1 @@
+428 players; last marble is worth 72061 points

AoC2018.Solutions/Day09/Marble.cs

@@ -0,0 +1,14 @@
+namespace AoC2018.Solutions.Day09
+{
+    using System.Diagnostics;
+
+    [DebuggerDisplay("{Number} : {CounterClockwise.Number} - {Number} - {Clockwise.Number}")]
+    public class Marble
+    {
+        public int Number { get; set; }
+
+        public Marble Clockwise { get; set; }
+
+        public Marble CounterClockwise { get; set; }
+    }
+}

AoC2018.Solutions/Day09/MarbleExtensions.cs

@@ -0,0 +1,86 @@
+namespace AoC2018.Solutions.Day09
+{
+    using System.Text;
+
+    public static class MarbleExtensions
+    {
+        public static Marble Clockwise(this Marble marble, int count)
+        {
+            Marble current = marble;
+            for (int i = 0; i < count; i++)
+            {
+                current = current.Clockwise;
+            }
+
+            return current;
+        }
+
+        public static Marble CounterClockwise(this Marble marble, int count)
+        {
+            Marble current = marble;
+            for (int i = 0; i < count; i++)
+            {
+                current = current.CounterClockwise;
+            }
+
+            return current;
+        }
+
+        public static Marble InsertAfter(this Marble marble, int number)
+        {
+            Marble next = marble.Clockwise;
+            var newMarble = new Marble
+            {
+                Number = number,
+                Clockwise = next,
+                CounterClockwise = marble,
+            };
+
+            marble.Clockwise = newMarble;
+            next.CounterClockwise = newMarble;
+
+            return newMarble;
+        }
+
+        public static Marble Remove(this Marble marble)
+        {
+            Marble prev = marble.CounterClockwise;
+            Marble next = marble.Clockwise;
+
+            prev.Clockwise = next;
+            next.CounterClockwise = prev;
+
+            marble.Clockwise = null;
+            marble.CounterClockwise = null;
+
+            return marble;
+        }
+
+        public static string Visualise(this Marble start, Marble current)
+        {
+            var visualisation = new StringBuilder();
+
+            Marble active = start;
+
+            do
+            {
+                if (active == current)
+                {
+                    visualisation.Append("(");
+                    visualisation.Append(active.Number);
+                    visualisation.Append(")");
+                }
+                else
+                {
+                    visualisation.Append(active.Number);
+                }
+
+                visualisation.Append(" ");
+                active = active.Clockwise;
+            }
+            while (active != start);
+
+            return visualisation.ToString();
+        }
+    }
+}

AoC2018.Solutions/Day09/Part01.cs

@@ -0,0 +1,56 @@
+namespace AoC2018.Solutions.Day09
+{
+    using System;
+    using System.Linq;
+
+    public class Part01 : ISolution
+    {
+        public string Solve(string input)
+        {
+            string[] components = input.Split(' ');
+
+            return this.Solve(int.Parse(components[0]), int.Parse(components[6])).ToString();
+        }
+
+        public long Solve(int players, int marbles)
+        {
+            long[] scores = new long[players];
+
+            // Set up Marble 0.
+            // We're going to solve this using a doubly linked list
+            var marble0 = new Marble
+            {
+                Number = 0,
+            };
+
+            marble0.Clockwise = marble0;
+            marble0.CounterClockwise = marble0;
+
+            Marble currentMarble = marble0;
+            int currentPlayer = 0;
+
+            for (int i = 1; i <= marbles; i++)
+            {
+                if (i % 23 == 0)
+                {
+                    // Current player keeps this marble
+                    scores[currentPlayer] += i;
+
+                    // Also keeps the marble 7 counter clockwise
+                    Marble marbleToRemove = currentMarble.CounterClockwise(7);
+                    currentMarble = marbleToRemove.Clockwise;
+                    scores[currentPlayer] += marbleToRemove.Number;
+                    marbleToRemove.Remove();
+                }
+                else
+                {
+                    currentMarble = currentMarble.Clockwise(1).InsertAfter(i);
+                }
+
+                currentPlayer = ++currentPlayer % players;
+            }
+
+            return scores.Max();
+        }
+    }
+}

AoC2018.Solutions/Day09/Part02.cs

@@ -0,0 +1,17 @@
+namespace AoC2018.Solutions.Day09
+{
+    using System;
+    using System.Linq;
+
+    public class Part02 : ISolution
+    {
+        public string Solve(string input)
+        {
+            var part1 = new Part01();
+
+            string[] components = input.Split(' ');
+
+            return part1.Solve(int.Parse(components[0]), int.Parse(components[6]) * 100).ToString();
+        }
+    }
+}

AoC2018.Tests/AoCTestCases.cs

@@ -55,5 +55,18 @@ public void Day07Part02()
             string result = solution.Solve("Step C must be finished before step A can begin.\r\nStep C must be finished before step F can begin.\r\nStep A must be finished before step B can begin.\r\nStep A must be finished before step D can begin.\r\nStep B must be finished before step E can begin.\r\nStep D must be finished before step E can begin.\r\nStep F must be finished before step E can begin.", 2, 0);
             Assert.That(result, Is.EqualTo("15"));
         }
+
+        [TestCase(9, 25, 32)]
+        [TestCase(10, 1618, 8317)]
+        [TestCase(13, 7999, 146373)]
+        [TestCase(17, 1104, 2764)]
+        [TestCase(21, 6111, 54718)]
+        [TestCase(30, 5807, 37305)]
+        public void Day09Part01(int players, int lastMarble, long expectedHighScore)
+        {
+            var solution = new AoC2018.Solutions.Day09.Part01();
+            long result = solution.Solve(players, lastMarble);
+            Assert.That(result, Is.EqualTo(expectedHighScore));
+        }
     }
 }