49 lines
1.3 KiB
C#
49 lines
1.3 KiB
C#
using System.IO;
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using System.Linq;
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using System.Numerics;
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namespace aoc2020
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{
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public sealed class Day3 : 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 Day3()
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{
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_grid = File.ReadLines("input/day3big.in").ToArray();
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_width = _grid[0].Length;
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}
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public override int DayNumber => 3;
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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()
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{
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return $"{CountSlope(3, 1)}";
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}
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public override string Part2()
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{
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var xSlops = new[] {2, 3, 4, 5, 8, 9, 12, 16, 18, 24, 32, 36, 48, 54, 65};
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var ySlops = new[] {1, 5, 7, 11, 13, 17, 19, 23, 25, 29, 31, 25, 37, 41, 47};
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return xSlops
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.SelectMany(x => ySlops, (x, y) => (x, y))
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.Select(s => CountSlope(s.Item1, s.Item2))
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.Select(s => new BigInteger(s))
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.Aggregate(BigInteger.Multiply)
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.ToString();
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}
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}
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}
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