52 lines
1.6 KiB
C#
52 lines
1.6 KiB
C#
namespace AOC2021;
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/// <summary>
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/// Day 17: <a href="https://adventofcode.com/2021/day/17"/>
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/// </summary>
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public sealed class Day17() : Day(2021, 17, "Trick Shot")
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{
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private List<int>? _target;
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public override void ProcessInput() =>
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_target = Input.First()
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.Split(' ', StringSplitOptions.TrimEntries | StringSplitOptions.RemoveEmptyEntries)
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.Skip(2)
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.SelectMany(i => i.Split('=')[1].Split(".."))
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.Select(i => i.TrimEnd(','))
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.Select(int.Parse)
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.ToList();
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public override object Part1()
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{
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var initialYVelocity = Math.Abs(_target![2]) - 1;
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return (initialYVelocity + 1) * initialYVelocity / 2;
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}
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public override object Part2()
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{
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var successfulVelocities = new HashSet<(int x, int y)>();
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var xMin = 1;
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while (xMin * (xMin + 1) / 2 < _target![0]) xMin++;
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for (var x = xMin; x <= _target[1]; x++)
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for (var y = _target[2]; y < Math.Abs(_target[2]); y++)
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{
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int xVelocity = x, yVelocity = y, xPos = 0, yPos = 0;
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while (xPos <= _target[1] && yPos >= _target[2])
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{
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xPos += xVelocity;
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yPos += yVelocity;
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if (xPos >= _target[0] && xPos <= _target[1] && yPos >= _target[2] && yPos <= _target[3])
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successfulVelocities.Add((x, y));
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xVelocity = xVelocity == 0 ? 0 : xVelocity - 1;
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yVelocity--;
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}
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}
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return successfulVelocities.Count;
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}
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}
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