One Elf has the important job of loading all of the rucksacks with supplies for the jungle journey. Unfortunately, that Elf didn't quite follow the packing instructions, and so a few items now need to be rearranged.

Each rucksack has two large compartments. All items of a given type are meant to go into exactly one of the two compartments. The Elf that did the packing failed to follow this rule for exactly one item type per rucksack.

Read the full puzzle.

using System;
using System.Collections.Generic;
using System.Linq;

namespace AdventOfCode.Y2022.Day03;

[ProblemName("Rucksack Reorganization")]
class Solution : Solver {

    public object PartOne(string input) =>
        // A line can be divided into two 'compartments' of equal length. We 
        // need to find the common item (letter) in them, and convert it to a 
        // number called 'priority'. Do this for each line and sum the 
        // priorities. 
        // We use 'chunk' to split a line in half.
        input.Split("\n")
            .Select(line => line.Chunk(line.Length/2)) // 🥩 
            .Select(GetCommonItemPriority)
            .Sum();

    public object PartTwo(string input) =>
        // Here we need to find the common item in three consecutive lines, 
        // convert it to priority as before, and sum it up along the whole 
        // input. 
        // This is again conveniently done using the chunk function.
        input.Split("\n")
            .Chunk(3)
            .Select(GetCommonItemPriority)
            .Sum();

    private int GetCommonItemPriority(IEnumerable<IEnumerable<char>> texts) => (
        from ch in texts.First()
        where texts.All(text => text.Contains(ch))
        select ch < 'a' ? ch - 'A' + 27 : ch - 'a' + 1
    ).First();

}

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