day 13

4 files changed, 1152 insertions, 0 deletions

diff --git a/aoc2021.test/DayTests.cs b/aoc2021.test/DayTests.cs
index 04b9d4f..4b27888 100644
--- a/aoc2021.test/DayTests.cs
+++ b/aoc2021.test/DayTests.cs
@@ -3,6 +3,23 @@ namespace aoc2021.test;
 [TestClass]
 public class DayTests
 {
+    private const string Day13Actual = @"
+████▒███▒▒████▒▒██▒▒█▒▒█▒▒██▒▒█▒▒█▒█▒▒█
+█▒▒▒▒█▒▒█▒▒▒▒█▒█▒▒█▒█▒█▒▒█▒▒█▒█▒▒█▒█▒▒█
+███▒▒█▒▒█▒▒▒█▒▒█▒▒▒▒██▒▒▒█▒▒▒▒████▒█▒▒█
+█▒▒▒▒███▒▒▒█▒▒▒█▒██▒█▒█▒▒█▒▒▒▒█▒▒█▒█▒▒█
+█▒▒▒▒█▒▒▒▒█▒▒▒▒█▒▒█▒█▒█▒▒█▒▒█▒█▒▒█▒█▒▒█
+████▒█▒▒▒▒████▒▒███▒█▒▒█▒▒██▒▒█▒▒█▒▒██▒
+";
+
+    private const string Day13Test = @"
+█████
+█▒▒▒█
+█▒▒▒█
+█▒▒▒█
+█████
+";
+
     [DataTestMethod]
     [DataRow(typeof(Day01), "1616", "1645")]
     [DataRow(typeof(Day02), "2272262", "2134882034")]
@@ -16,6 +33,7 @@ public class DayTests
     [DataRow(typeof(Day10), "288291", "820045242")]
     [DataRow(typeof(Day11), "1613", "510")]
     [DataRow(typeof(Day12), "4549", "120535")]
+    [DataRow(typeof(Day13), "837", Day13Actual)]
     public void CheckAllDays(Type dayType, string part1, string part2)
     {
         var s = Stopwatch.StartNew();
@@ -58,6 +76,7 @@ public class DayTests
     [DataRow(typeof(Day10), "26397", "288957")]
     [DataRow(typeof(Day11), "1656", "195")]
     [DataRow(typeof(Day12), "226", "3509")]
+    [DataRow(typeof(Day13), "17", Day13Test)]
     public void CheckTestInputs(Type dayType, string part1, string part2)
     {
         Day.UseTestInput = true;
diff --git a/aoc2021/Day13.cs b/aoc2021/Day13.cs
new file mode 100644
index 0000000..1ad9016
--- /dev/null
+++ b/aoc2021/Day13.cs
@@ -0,0 +1,82 @@
+using MoreLinq;
+
+namespace aoc2021;
+
+/// <summary>
+/// Day 13: <see href="https://adventofcode.com/2021/day/13"/>
+/// </summary>
+public sealed class Day13 : Day
+{
+    private List<(int x, int y)> _grid;
+    private readonly List<(char axis, int index)> _folds;
+    
+    public Day13() : base(13, "Transparent Origami")
+    {
+        var s = Input.Split("").ToList();
+        
+        _grid = s[0].Select(p =>
+        {
+            var i = p.Split(',', 2).Select(int.Parse).ToList();
+            return (i[0], i[1]);
+        }).ToList();
+        
+        _folds = s[1].Select(p => p.Split(' ').Skip(2).First()).Select(p =>
+        {
+            var i = p.Split('=', 2);
+            return (i[0][0], int.Parse(i[1]));
+        }).ToList();
+    }
+    
+    private static List<(int x, int y)> DoFold(List<(int x, int y)> grid, char axis, int at)
+    {
+        List<(int, int)> result = new();
+        
+        switch (axis)
+        {
+            case 'x':
+                foreach (var (x, y) in grid)
+                    result.Add((x > at ? 2 * at - x : x, y));
+                break;
+            case 'y':
+                foreach (var (x, y) in grid)
+                    result.Add((x, y > at ? 2 * at - y : y));
+                break;
+            default:
+                throw new ArgumentException("invalid fold axis", nameof(axis));
+        }
+
+        return result.Distinct().ToList();
+    }
+
+    private string PrintGrid()
+    {
+        var xMax = _grid.Max(g => g.x);
+        var yMax = _grid.Max(g => g.y);
+        var s = new StringBuilder();
+
+        for (var y = 0; y <= yMax; y++)
+        {
+            for (var x = 0; x <= xMax; x++)
+                s.Append(_grid.Contains((x, y)) ? "█" : "▒");
+
+            s.AppendLine();
+        }
+
+        return s.ToString();
+    }
+
+    public override object Part1()
+    {
+        var (axis, at) = _folds[0];
+        var foldedOnce = DoFold(_grid, axis, at);
+        return foldedOnce.Count;
+    }
+
+    public override object Part2()
+    {
+        foreach (var (axis, at) in _folds)
+            _grid = DoFold(_grid, axis, at);
+
+        return Environment.NewLine + PrintGrid();
+    }
+}
diff --git a/aoc2021/input/day13.in b/aoc2021/input/day13.in
new file mode 100644
index 0000000..4205957
--- /dev/null
+++ b/aoc2021/input/day13.in
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+1195,301
+155,541
+508,194
+1305,576
+1207,38
+691,414
+262,609
+962,529
+54,19
+796,4
+365,441
+913,79
+100,469
+95,763
+1053,563
+390,515
+1168,302
+142,190
+802,252
+1113,215
+490,344
+1253,483
+552,546
+517,562
+550,359
+326,166
+1166,823
+542,708
+500,850
+512,592
+817,383
+166,758
+1141,654
+166,408
+768,131
+316,316
+589,148
+490,812
+1010,777
+
+fold along x=655
+fold along y=447
+fold along x=327
+fold along y=223
+fold along x=163
+fold along y=111
+fold along x=81
+fold along y=55
+fold along x=40
+fold along y=27
+fold along y=13
+fold along y=6
diff --git a/aoc2021/input/test13.in b/aoc2021/input/test13.in
new file mode 100644
index 0000000..32a8563
--- /dev/null
+++ b/aoc2021/input/test13.in
@@ -0,0 +1,21 @@
+6,10
+0,14
+9,10
+0,3
+10,4
+4,11
+6,0
+6,12
+4,1
+0,13
+10,12
+3,4
+3,0
+8,4
+1,10
+2,14
+8,10
+9,0
+
+fold along y=7
+fold along x=5
\ No newline at end of file