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Day03.cs
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Day03.cs
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using System;
using System.Runtime.CompilerServices;
using AdventOfCode.CSharp.Common;
namespace AdventOfCode.CSharp.Y2020.Solvers;
public class Day03 : ISolver
{
public static void Solve(ReadOnlySpan<byte> input, Solution solution)
{
int w = input.IndexOf((byte)'\n');
int h = (input.Length + 1) / (w + 1);
long slope_1_1 = CountTrees(input, w, h, 1, 1);
long slope_3_1 = CountTrees(input, w, h, 3, 1);
long slope_5_1 = CountTrees(input, w, h, 5, 1);
long slope_7_1 = CountTrees(input, w, h, 7, 1);
long slope_1_2 = CountTrees(input, w, h, 1, 2);
long part1 = slope_3_1;
long part2 = slope_1_1 * slope_3_1 * slope_5_1 * slope_7_1 * slope_1_2;
solution.SubmitPart1(part1);
solution.SubmitPart2(part2);
}
[MethodImpl(MethodImplOptions.AggressiveInlining)]
static long CountTrees(ReadOnlySpan<byte> input, int w, int h, int dx, int dy)
{
int stride = w + 1;
int x = 0;
long total = 0;
for (int y = 0; y < h; y += dy)
{
if (input[y * stride + x] == '#')
{
total += 1;
}
x += dx;
if (x >= w)
x -= w;
}
return total;
}
}