Space needs to be cleared before the last supplies can be unloaded from the ships, and so several Elves have been assigned the job of cleaning up sections of the camp. Every section has a unique ID number, and each Elf is assigned a range of section IDs.

However, as some of the Elves compare their section assignments with each other, they've noticed that many of the assignments overlap. To try to quickly find overlaps and reduce duplicated effort, the Elves pair up and make a big list of the section assignments for each pair (your puzzle input).

Read the full puzzle.

using System;
using System.Linq;

namespace AdventOfCode.Y2022.Day04;

[ProblemName("Camp Cleanup")]
class Solution : Solver {
    
    // Each line of the input represents two ranges - job done by two elves.
    // We need to find those lines where the elves did some work twice.
    // Part 1 and 2 differs in how we define 'duplicated work'.
    record struct Range(int from, int to);

    public object PartOne(string input) => DuplicatedWorkCount(input, Contains);
    public object PartTwo(string input) => DuplicatedWorkCount(input, Overlaps);

    // True if r1 contains r2 [ { } ] 
    bool Contains(Range r1, Range r2) => r1.from <= r2.from && r2.to <= r1.to; 
    
    // True if r1 overlaps r2 { [ } ], the other direction is not checked.
    bool Overlaps(Range r1, Range r2) => r1.to >= r2.from && r1.from <= r2.to; 

    // DuplicatedWorkCount parses each input line into ranges and applies 
    // rangeCheck on them to find duplicated work. RangeCheck doesnt have to be 
    // symmetrical in its arguments, but DuplicatedWorkCount makes it so calling
    // it twice with the arguments swapped.
    private int DuplicatedWorkCount(
        string input, 
        Func<Range, Range, bool> rangeCheck
    ) {
        // E.g. '36-41,35-40' becomes [Range(36, 41), Range(35, 40)]
        var parseRanges = (string line) => 
            from range in line.Split(',') 
            let fromTo = range.Split('-').Select(int.Parse)
            select new Range(fromTo.First(), fromTo.Last());

        return input
            .Split("\n")
            .Select(parseRanges)
            .Count(ranges => 
                rangeCheck(ranges.First(), ranges.Last()) || 
                rangeCheck(ranges.Last(), ranges.First())
            );
    }
}

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