90 lines
2.4 KiB
C#
90 lines
2.4 KiB
C#
namespace aoc2020;
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/// <summary>
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/// Day 12: <see href="https://adventofcode.com/2020/day/12" />
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/// </summary>
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public sealed class Day12 : Day
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{
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public Day12() : base(12, "Rain Risk")
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{
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}
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private static void Swap(ref int x, ref int y)
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{
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(y, x) = (x, y);
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}
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private (int x, int y, int sx, int sy) ProcessInstructions()
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{
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// start facing east
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int x = 0, y = 0, dx = 1, dy = 0;
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int sx = 0, sy = 0, waypointX = 10, waypointY = -1;
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foreach (var instruction in Input)
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{
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var value = int.Parse(instruction[1..]);
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switch (instruction[0])
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{
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case 'N':
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y -= value;
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waypointY -= value;
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break;
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case 'S':
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y += value;
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waypointY += value;
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break;
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case 'E':
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x += value;
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waypointX += value;
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break;
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case 'W':
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x -= value;
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waypointX -= value;
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break;
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case 'L':
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for (var i = 0; i < value / 90; ++i)
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{
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Swap(ref dx, ref dy);
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Swap(ref waypointX, ref waypointY);
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dy *= -1;
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waypointY *= -1;
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}
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break;
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case 'R':
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for (var i = 0; i < value / 90; ++i)
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{
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Swap(ref dx, ref dy);
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Swap(ref waypointX, ref waypointY);
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dx *= -1;
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waypointX *= -1;
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}
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break;
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case 'F':
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x += dx * value;
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y += dy * value;
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sx += waypointX * value;
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sy += waypointY * value;
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break;
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default: throw new InvalidOperationException(nameof(instruction));
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}
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}
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return (x, y, sx, sy);
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}
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public override string Part1()
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{
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var (x, y, _, _) = ProcessInstructions();
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return $"{Math.Abs(x) + Math.Abs(y)}";
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}
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public override string Part2()
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{
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var (_, _, sx, sy) = ProcessInstructions();
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return $"{Math.Abs(sx) + Math.Abs(sy)}";
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}
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}
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