AdventOfCode/AdventOfCode.Solutions/2023/Day 15/Day15.cs

using AdventOfCode.Core.Shared.IO;
using System.Text;

namespace AdventOfCode.Solutions._2023
{
    public class Day15 : IChallange
    {
        public int Year => 2023;
        public int Day => 15;

        private readonly IInputReader _inputReader;

        public Day15(IInputReader inputReader)
        {
            _inputReader = inputReader;
            _inputReader.SetInput(this);
        }

        public async Task<string> GetSolutionPart1()
        {
            string[] data = (await _inputReader.ReadAsString()).Split(',', StringSplitOptions.RemoveEmptyEntries);
            int stringTotal = 0;
            foreach (string s in data)
            {
                stringTotal += GetHash(s);
            }
            return stringTotal.ToString();
        }

        public async Task<string> GetSolutionPart2()
        {
            string[] data = (await _inputReader.ReadAsString()).Split(',', StringSplitOptions.RemoveEmptyEntries);
            Dictionary<int, List<(string Label, int FocusLength)>> boxes = [];
            foreach (string s in data)
            {
                if (s.EndsWith('-'))
                {
                    string label = s[..^1];
                    // remove
                    int box = GetHash(label);
                    if (boxes.TryGetValue(box, out var lensBox))
                    {
                        var currentLens = lensBox.FirstOrDefault(l => l.Label == label);
                        if (!string.IsNullOrEmpty(currentLens.Label))
                        {
                            lensBox.Remove(currentLens);
                        }
                    }

                    continue;
                }

                if (char.IsDigit(s[^1]))
                {
                    string label = s[..^2];
                    int box = GetHash(label);
                    int newFocal = int.Parse($"{s[^1]}");
                    if (boxes.TryGetValue(box, out var lensBox))
                    {
                        var newLens = (label, newFocal);
                        var currentLens = lensBox.FirstOrDefault(l => l.Label == label);
                        if (!string.IsNullOrEmpty(currentLens.Label))
                        {
                            int index = lensBox.IndexOf(currentLens);
                            lensBox[index] = newLens;
                        }
                        else
                        {
                            lensBox.Add(newLens);
                        }
                    }
                    else
                    {
                        boxes.Add(box, [(label, newFocal)]);
                    }
                }
            }

            int total = 0;

            foreach(var box in boxes)
            {
                total += GetBoxValue(box.Key + 1, box.Value);
            }

            return total.ToString();
        }

        private static int GetBoxValue(int boxId, List<(string Label, int FocusLength)> box) => box.Select((kvp, index) => boxId * (index + 1) * kvp.FocusLength).Sum();

        private static int GetBoxValue(Dictionary<string, int> box) => box.Select((kvp, index) => (index + 1) * kvp.Value).Sum();

        private static int GetHash(string s)
        {
            int segementTotal = 0;
            foreach (byte value in Encoding.ASCII.GetBytes(s))
            {
                segementTotal += value;
                segementTotal *= 17;
                segementTotal %= 256;
            }
            return segementTotal;
        }
    }
}