Add AoC 2025 project structure and first solutions

2025-12-04 21:40:42 +01:00
parent c83642d286
commit 1e98d90c33
15 changed files with 754 additions and 0 deletions
@@ -0,0 +1,102 @@
+using System.Collections.Generic;
+using System.IO;
+using System.Linq;
+using AdvenOfCode.Contracts;
+using Coordinate = (int x, int y);
+
+namespace AoC_2025;
+
+public class Day04 : IPuzzleSolver<long>
+{
+    private string[] ParsePuzzleInput(string path)
+    {
+        var puzzleInput = File.ReadAllLines(path)
+            .Where(line => !string.IsNullOrWhiteSpace(line))
+            .Select(line => line.Trim())
+            .ToArray();
+        return puzzleInput;
+    }
+
+    public long SolvePart1(string pathToPuzzleInput)
+    {
+        var paperrollGrid = ParsePuzzleInput(pathToPuzzleInput);
+        var accessiblePaperrolls = GetAccessiblePaperrolls(paperrollGrid);
+        var countAccessibleRolls = accessiblePaperrolls.Count();
+        return countAccessibleRolls;
+    }
+    
+    public long SolvePart2(string pathToPuzzleInput)
+    {
+        var paperrollGrid = ParsePuzzleInput(pathToPuzzleInput);
+        var rollCoordinates = GetRollCoordinates(paperrollGrid);
+        var countAccessibleRolls = RecursiveCountAllRemovableRolls(rollCoordinates);
+        return countAccessibleRolls;
+    }
+
+    private IEnumerable<Coordinate> GetAccessiblePaperrolls(IEnumerable<string> paperrollGrid)
+    {
+        var rollCoordinates = GetRollCoordinates(paperrollGrid);
+        var rollsWithNeighbours = GetNeighbours(rollCoordinates);
+        var accessiblePaperrolls = FilterForLessThan(rollsWithNeighbours, 4);
+        return accessiblePaperrolls;
+    }
+    
+    private int RecursiveCountAllRemovableRolls(HashSet<Coordinate> coordinates)
+    {
+        var rollsWithNeighbours = GetNeighbours(coordinates);
+        var accessiblePaperrolls = FilterForLessThan(rollsWithNeighbours, 4).ToArray();
+        var countAccessibleRolls = accessiblePaperrolls.Length;
+        coordinates.ExceptWith(accessiblePaperrolls);
+        return countAccessibleRolls == 0
+            ? 0
+            : countAccessibleRolls + RecursiveCountAllRemovableRolls(coordinates);
+    }
+
+    private HashSet<Coordinate> GetRollCoordinates(IEnumerable<string> paperrollGrid)
+    {
+        var coordinates = paperrollGrid
+            .SelectMany((gridLine, xIndex) => GetCoordinates(gridLine, xIndex))
+            .ToHashSet();
+        return coordinates;
+    }
+
+    private IEnumerable<Coordinate> GetCoordinates(string gridLine, int xIndex)
+    {
+        var indexedCharacters = gridLine.Select((character, yIndex) => (character, yIndex));
+        var validRolls = indexedCharacters.Where(tuple => tuple.character == '@');
+        var rollCoordinates = validRolls.Select(tuple => (xIndex, tuple.yIndex));
+        return rollCoordinates;
+    }
+
+    private IEnumerable<(Coordinate coordinate, Coordinate[] neighbours)> GetNeighbours(HashSet<Coordinate> rollCoordinates)
+    {
+        var coordsWithNeighbourCount = rollCoordinates
+            .Select(coord => (coord, GetNeighbours(coord, rollCoordinates)));
+        return coordsWithNeighbourCount;
+    }
+
+    private Coordinate[] GetNeighbours(Coordinate coordinate, HashSet<Coordinate> coordinates)
+    {
+        Coordinate[] neighbourDirections =
+        [
+            (-1, -1), (-1, 0), (-1, 1),
+            (0, -1), (0, 1),
+            (1, -1), (1, 0), (1, 1),
+        ];
+        var possibleNeighbours = neighbourDirections
+            .Select(direction => (coordinate.x + direction.x, coordinate.y + direction.y));
+        var actualNeighbours = possibleNeighbours
+            .Where(coord => coordinates.Contains(coord))
+            .ToArray();
+        return actualNeighbours;
+    }
+
+    private IEnumerable<Coordinate> FilterForLessThan(IEnumerable<(Coordinate coordinate, Coordinate[] neighbours)> coordinatesWithNeighbours,
+        int lessThan)
+    {
+        var coordinatesWithLess = coordinatesWithNeighbours
+            .Where(entry => entry.neighbours.Count() < lessThan)
+            .Select(entry => entry.coordinate);
+        return coordinatesWithLess;
+    }
+}