[2k25] Add day 4

2025-12-04 21:35:12 +01:00
parent a805b5b96a
commit 04102d1fec
4 changed files with 297 additions and 1 deletions
--- a/Days/Day4.cs
+++ b/Days/Day4.cs
@@ -0,0 +1,156 @@
+using Spectre.Console;
+
+namespace AdventOfCode.Days;
+
+public class Day4 : Day
+{
+    public override int Number => 4;
+    public override string Name => "Printing Department";
+
+    public const int Length = 136;
+
+    public override void RunPart1(bool display = true)
+    {
+        var accessibleRollsOfPaper = 0;
+
+        var map = ParseMap(Input);
+
+        Span<(int i, int j)> adjacentPositions =
+        [
+            (-1, -1), (-1, 0), (-1, 1),
+            ( 0, -1),              ( 0, 1),
+            ( 1, -1), ( 1, 0), ( 1, 1)
+        ];
+
+        for (var i = 0; i < Length; i++)
+        {
+            for (var j = 0; j < Length; j++)
+            {
+                // There is no paper roll at position (i, j)
+                if (!map[i, j])
+                {
+                    continue;
+                }
+
+                // Check if a paper roll is accessible
+                var adjacentRolls = 0;
+                foreach (var adjacentPosition in adjacentPositions)
+                {
+                    var targetI = i + adjacentPosition.i;
+                    var targetJ = j + adjacentPosition.j;
+
+                    // Check that the adjacent position is not out of bounds
+                    if (targetI is < 0 or >= Length || targetJ is < 0 or >= Length)
+                    {
+                        continue;
+                    }
+
+                    if (map[targetI, targetJ])
+                    {
+                        adjacentRolls++;
+                    }
+                }
+
+                if (adjacentRolls < 4)
+                {
+                    accessibleRollsOfPaper++;
+                }
+            }
+        }
+
+        if (display)
+        {
+            AnsiConsole.MarkupLine($"[green]Accessible rolls of paper: [yellow]{accessibleRollsOfPaper}[/][/]");
+        }
+    }
+
+    public override void RunPart2(bool display = true)
+    {
+        var accessibleRollsOfPaper = 0;
+
+        var map = ParseMap(Input);
+
+        Span<(int i, int j)> adjacentPositions =
+        [
+            (-1, -1), (-1, 0), (-1, 1),
+            ( 0, -1),              ( 0, 1),
+            ( 1, -1), ( 1, 0), ( 1, 1)
+        ];
+
+        int removedRollsOfPaper;
+        // Loop until we cannot remove any roll anymore
+        do
+        {
+            removedRollsOfPaper = 0;
+
+            for (var i = 0; i < Length; i++)
+            {
+                for (var j = 0; j < Length; j++)
+                {
+                    // There is no paper roll at position (i, j)
+                    if (!map[i, j])
+                    {
+                        continue;
+                    }
+
+                    // Check if a paper roll is accessible
+                    var adjacentRolls = 0;
+                    foreach (var adjacentPosition in adjacentPositions)
+                    {
+                        var targetI = i + adjacentPosition.i;
+                        var targetJ = j + adjacentPosition.j;
+
+                        // Check that the adjacent position is not out of bounds
+                        if (targetI is < 0 or >= Length || targetJ is < 0 or >= Length)
+                        {
+                            continue;
+                        }
+
+                        if (map[targetI, targetJ])
+                        {
+                            adjacentRolls++;
+                        }
+                    }
+
+                    if (adjacentRolls < 4)
+                    {
+                        removedRollsOfPaper++;
+
+                        // Remove roll of paper
+                        map[i, j] = false;
+                    }
+                }
+            }
+
+            accessibleRollsOfPaper += removedRollsOfPaper;
+        } while (removedRollsOfPaper > 0);
+
+        if (display)
+        {
+            AnsiConsole.MarkupLine($"[green]Accessible rolls of paper: [yellow]{accessibleRollsOfPaper}[/][/]");
+        }
+    }
+
+    private static bool[,] ParseMap(string input)
+    {
+        // Map is a  square
+        var map = new bool[Length, Length];
+
+        var i = 0;
+        foreach (var line in input.EnumerateLines())
+        {
+            var j = 0;
+
+            foreach (var value in line)
+            {
+                map[i, j] = value is '@';
+
+                j++;
+            }
+
+            i++;
+        }
+
+        return map;
+    }
+}