40 lines
968 B
C#
40 lines
968 B
C#
namespace AOC2020;
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/// <summary>
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/// Day 3: <see href="https://adventofcode.com/2020/day/3" />
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/// </summary>
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public sealed class Day03 : Day
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{
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private readonly string[] _grid;
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private readonly int _width;
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public Day03() : base(2020, 3, "Toboggan Trajectory")
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{
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_grid = Input.ToArray();
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_width = _grid[0].Length;
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}
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private long CountSlope(int dx, int dy)
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{
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long hits = 0;
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for (int x = 0, y = 0; y < _grid.Length; y += dy, x = (x + dx) % _width)
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if (_grid[y][x] == '#')
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hits++;
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return hits;
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}
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public override string Part1() => $"{CountSlope(3, 1)}";
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public override string Part2()
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{
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var xSlopes = new[] { 1, 3, 5, 7, 1 };
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var ySlopes = new[] { 1, 1, 1, 1, 2 };
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return xSlopes.Zip(ySlopes)
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.Select(s => CountSlope(s.First, s.Second))
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.Aggregate((acc, i) => acc * i)
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.ToString();
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}
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}
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