75 lines
2.3 KiB
C#
75 lines
2.3 KiB
C#
using System;
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using System.Collections.Generic;
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using System.Linq;
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using aoc2019.lib;
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namespace aoc2019
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{
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internal sealed class Day10 : Day
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{
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private readonly HashSet<(int x, int y)> asteroids = new HashSet<(int x, int y)>();
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private (int x, int y) best = (x: -1, y: -1);
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private int bestcansee;
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public Day10()
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{
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asteroids = Input
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.Select((r, y) => r.Select((c, x) => (x, y, isAsteroid: c == '#')).ToArray())
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.SelectMany(r => r)
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.Where(a => a.isAsteroid)
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.Select(a => (a.x, a.y))
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.ToHashSet();
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}
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public override int DayNumber => 10;
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public override string Part1()
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{
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foreach (var asteroid in asteroids)
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{
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var cansee = asteroids
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.Except(new[] {asteroid})
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.Select(a => (x: a.x - asteroid.x, y: a.y - asteroid.y))
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.GroupBy(a => Math.Atan2(a.y, a.x))
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.Count();
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if (cansee > bestcansee)
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{
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best = asteroid;
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bestcansee = cansee;
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}
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}
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return $"{bestcansee}";
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}
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public override string Part2()
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{
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static IEnumerable<(int x, int y, double angle, double dist)> GetValue(
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Queue<(int x, int y, double angle, double dist)> q)
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{
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if (q.Count > 0) yield return q.Dequeue();
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}
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return asteroids
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.Where(a => a != best)
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.Select(a =>
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{
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var xdist = a.x - best.x;
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var ydist = a.y - best.y;
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var angle = Math.Atan2(xdist, ydist);
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return (a.x, a.y, angle, dist: Math.Sqrt(xdist * xdist + ydist * ydist));
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})
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.ToLookup(a => a.angle)
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.OrderByDescending(a => a.Key)
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.Select(a => new Queue<(int x, int y, double angle, double dist)>(a.OrderBy(b => b.dist)))
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.Repeat()
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.SelectMany(GetValue)
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.Skip(199)
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.Take(1)
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.Select(a => a.x * 100 + a.y)
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.Single()
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.ToString();
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}
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}
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} |