FSharp

I'm a month late, but eh. Compared to everyone else, it looks like my approach of preserving duplicates was unnecessary. I chose to use SortedSets (redundant since I sort the inputs) and cascade to the next best fit. The sorted sets also let me grab the Max/Min values and I thought that it was more in line with the intention than having a list that happens to be sorted.

I also sorted part 1 based on what I thought was the best fit, which was the same solution for part 3.
For part 2 I duplicated part 1's logic but reversed the order to asc instead of desc, but I don't know that that made a difference and excluded it here. The only difference is the "add if count < 20".

type Crate = int  
 // sorted set because only one item can be in at a time. The SortedSet is unnecessary here since the inputs are already sorted  
type CrateSet = SortedSet<Crate>  
let inline newCrateSet crate =  
    let cs = CrateSet()  
    cs.Add(crate) |> ignore  
    cs  
type Extensions() =  
    [<Extension>]  
    static member inline SmallestCrate (crates:CrateSet) : Crate option = match crates.Min with | 0 -> None | x -> Some x  
    [<Extension>]  
    static member inline LargestCrate (crates:CrateSet) : Crate option = match crates.Max with | 0 -> None | x -> Some x  

/// take a sorted input (not verified) and prioritize insertion into the first found list.  
/// This results in cascading to the "next best fit", but this approach relies on sorted inputs.  
let packEfficiently allCrates =  
    allCrates  
    |> Seq.fold (fun sortedCrates next ->  
            // find the first crate set that can hold the next item and put it in there  
            match sortedCrates with  
            | [] -> [newCrateSet next]  
            | items ->  
                match List.tryFind (fun (i:CrateSet) ->  
                    match i.SmallestCrate() with  
                    | Some c when c > next -> true  
                    | _ -> false) items with  
                | None ->  
                    let cs = newCrateSet next  
                    items@[cs] // appending to the end is less efficient for linked lists, but ensures that the first one gets the best goodies  
                | Some crates ->  
                    if not (crates.Add(next)) then failwith "failed to add" // really wrong if this happens  
                    items  

        ) []  

let part1 () =  
    parseInput "Inputs/Quest03/Q03_P01.txt"  
    |> Enumerable.OrderDescending  
    |> packEfficiently  
    |> _.Max(_.Sum())  

let part2() =  
    parseInput "Inputs/Quest03/Q03_P02.txt"  
    |> Enumerable.Order  
    |> part2Impl  
    |> List.filter (fun x -> x.Count = 20)  
    |> _.Min(_.Sum())  
    
let part3() =  
    parseInput "Inputs/Quest03/Q03_P03.txt"  
    |> Enumerable.OrderDescending  
    |> packEfficiently  
    |> _.Count()