65 lines
1.9 KiB
C#
65 lines
1.9 KiB
C#
namespace AOC2019;
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public sealed class Day10() : Day(2019, 10, "Monitoring Station")
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{
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private HashSet<(int x, int y)>? _asteroids;
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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 override void ProcessInput() =>
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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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public override object 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 object Part2()
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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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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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}
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}
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