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