advent-2024-01.cs

using System.Numerics;
using System.Runtime.InteropServices;

using var reader = new StreamReader("input.txt");
List<int> left = [], right = [];

while (reader.ReadLine() is string line)
{
    var lineSpan = line.AsSpan();

    var l = lineSpan[0..line.IndexOf(' ')];
    var r = lineSpan[(line.LastIndexOf(' ') + 1)..];

    left.Add(int.Parse(l));
    right.Add(int.Parse(r));
}

left.Sort();
right.Sort();

ReadOnlySpan<int> ls = CollectionsMarshal.AsSpan(left);
ReadOnlySpan<int> rs = CollectionsMarshal.AsSpan(right);

int distance = 0;

for (int i = 0; i < left.Count; i += Vector<int>.Count)
{
    distance += Vector.Sum(
        Vector.Abs(
            Vector.Subtract(
                new Vector<int>(ls[i..(i + Vector<int>.Count)]),
                new Vector<int>(rs[i..(i + Vector<int>.Count)]))));
}

Console.WriteLine(distance);