113 lines
2.7 KiB
C#
113 lines
2.7 KiB
C#
namespace AOC2019;
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public sealed class Day12 : Day
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{
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private readonly List<Position> _moons;
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private int _step;
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public Day12() : base(2019, 12, "The N-Body Problem")
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{
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_moons = Input
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.Select(moon =>
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moon
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.TrimStart('<')
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.TrimEnd('>')
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.Split(",")
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.Select(val => int.Parse(val.Split("=").Last()))
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)
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.Select(moon => new Position(moon.ToList()))
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.ToList();
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foreach (var moon in _moons)
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moon.SetSiblings(_moons);
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}
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private void Step()
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{
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foreach (var moon in _moons)
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moon.Gravitate();
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foreach (var moon in _moons)
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moon.Move();
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_step++;
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}
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public override string Part1()
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{
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while (_step < 1000)
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Step();
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return $"{_moons.Sum(p => p.TotalEnergy)}";
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}
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public override string Part2()
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{
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int cycleX = 0, cycleY = 0, cycleZ = 0;
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while (cycleX == 0 || cycleY == 0 || cycleZ == 0)
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{
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Step();
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if (cycleX == 0 && _moons.All(m => m.Dx == 0)) cycleX = _step * 2;
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if (cycleY == 0 && _moons.All(m => m.Dy == 0)) cycleY = _step * 2;
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if (cycleZ == 0 && _moons.All(m => m.Dz == 0)) cycleZ = _step * 2;
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}
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return $"{Util.Lcm(cycleX, Util.Lcm(cycleY, cycleZ))}";
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}
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public class Position
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{
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public int Dx, Dy, Dz;
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private List<Position> _siblings;
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private int _x, _y, _z;
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public Position(IList<int> moon)
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{
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_x = moon[0];
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_y = moon[1];
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_z = moon[2];
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Dx = 0;
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Dy = 0;
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Dz = 0;
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_siblings = new();
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}
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private int KineticEnergy =>
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Math.Abs(_x) + Math.Abs(_y) + Math.Abs(_z);
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private int PotentialEnergy =>
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Math.Abs(Dx) + Math.Abs(Dy) + Math.Abs(Dz);
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internal int TotalEnergy =>
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KineticEnergy * PotentialEnergy;
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public void SetSiblings(IEnumerable<Position> positions)
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{
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_siblings = positions.Where(p => p != this).ToList();
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}
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public override string ToString()
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{
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return $"pos=<x={_x}, y={_y}, z={_z}> vel=<x={Dx}, y={Dy}, z={Dz}>";
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}
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internal void Gravitate()
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{
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foreach (var m in _siblings)
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{
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if (_x != m._x) Dx += _x > m._x ? -1 : 1;
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if (_y != m._y) Dy += _y > m._y ? -1 : 1;
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if (_z != m._z) Dz += _z > m._z ? -1 : 1;
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}
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}
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internal void Move()
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{
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_x += Dx;
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_y += Dy;
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_z += Dz;
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}
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}
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}
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