111 lines
3.6 KiB
C#
111 lines
3.6 KiB
C#
using System;
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using System.Collections.Generic;
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using System.Linq;
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namespace aoc2020
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{
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/// <summary>
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/// Day 20: <see href="https://adventofcode.com/2020/day/20" />
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/// </summary>
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public sealed class Day20 : Day
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{
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private readonly List<Tile> _allPermutations;
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private readonly List<Tile> _topLefts;
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public Day20() : base(20, "Jurassic Jigsaw")
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{
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var lines = new List<string>();
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var tiles = new List<Tile>();
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var currentTileId = 0;
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foreach (var line in Input)
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if (line.StartsWith("Tile "))
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{
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currentTileId = int.Parse(line.Split(' ', ':')[1]);
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}
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else if (line == "")
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{
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tiles.Add(new(currentTileId, lines.Select(l => l.ToCharArray()).ToArray()));
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lines.Clear();
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}
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else
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{
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lines.Add(line);
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}
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if (lines.Any()) tiles.Add(new(currentTileId, lines.Select(l => l.ToCharArray()).ToArray()));
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_allPermutations = tiles.SelectMany(t => t.AllPermutations()).ToList();
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_topLefts = _allPermutations
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.Where(t => !_allPermutations.Any(t2 => t.TileId != t2.TileId && t.LeftId == t2.RightId) &&
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!_allPermutations.Any(t2 => t.TileId != t2.TileId && t.TopId == t2.BottomId))
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.ToList();
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}
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}
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public override string Part1()
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{
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return $"{_topLefts.Select(t => t.TileId).Distinct().Aggregate(1L, (acc, next) => acc * next)}";
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}
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public override string Part2()
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{
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return "";
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}
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private record Tile(int TileId, char[][] Pixels)
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{
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private const int Size = 10;
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internal int TopId => GetId(z => (z, 0));
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internal int BottomId => GetId(z => (z, Size - 1));
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internal int LeftId => GetId(z => (0, z));
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internal int RightId => GetId(z => (Size - 1, z));
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private int GetId(Func<int, (int x, int y)> selector)
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{
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return Enumerable.Range(0, Size)
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.Select(selector)
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.Select((c, i) => (Pixels[c.x][c.y] == '#' ? 1 : 0) << i)
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.Aggregate(0, (acc, next) => acc | next);
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}
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private Tile RotateClockwise()
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{
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return Transform((x, y, newPixels) => newPixels[x][Size - 1 - y] = Pixels[y][x]);
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}
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private Tile Flip()
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{
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return Transform((x, y, newPixels) => newPixels[y][Size - 1 - x] = Pixels[y][x]);
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}
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private Tile Transform(Action<int, int, char[][]> transformFunc)
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{
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var newPixels = Enumerable.Repeat(false, Size).Select(_ => new char[Size]).ToArray();
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for (var y = 0; y < Size; y++)
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for (var x = 0; x < Size; x++)
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transformFunc(x, y, newPixels);
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return new(TileId, newPixels);
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}
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internal IEnumerable<Tile> AllPermutations()
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{
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var tile = this;
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for (var i = 1; i <= 8; i++)
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{
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yield return tile;
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if (i == 4) tile = Flip();
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else if (i == 8) yield break;
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tile = tile.RotateClockwise();
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}
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}
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public string Format()
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{
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return $"Tile {TileId}:\n{string.Join("\n", Pixels.Select(p => new string(p)))}";
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}
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}
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}
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} |