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Contents
(* Based off the Haskell solution by Tarmean at http://exercism.io/submissions/6dc2eef7e7eb469d8657111fc4389fc0 *)
open Core.Std
type dominoe = int * int
(* Functions from Haskell that I can't find in Core! *)
let zip_with (xs: 'a list) (ys: 'b list) ~(f: 'a -> 'b -> 'c) =
let rec go xs ys acc = match (xs,ys) with
| (x::xs,y::ys) -> go xs ys @@ (f x y)::acc
| _ -> acc
in
List.rev @@ go xs ys []
let tails (xs: 'a list): ('a list) list =
let rec go acc = function
| [] -> [] :: acc
| (_::xs) as l -> go (l :: acc) xs
in
List.rev @@ go [] xs
let inits (xs: 'a list): ('a list) list =
List.rev xs |> tails |> List.map ~f:List.rev |> List.rev
let listToOption = function
| [] -> None
| (x :: _) -> Some x
(* The implementation *)
let left (ds: dominoe list): int = ds |> List.hd_exn |> fst
let right (ds: dominoe list): int = ds |> List.last_exn |> snd
let choose_from (ls: 'a list): ('a * 'a list) list =
List.zip_exn ls @@ zip_with ~f:List.append (inits ls) (List.tl_exn (tails ls))
let rec attach_to path ((a, b), rest) =
let lp = left path in
if b = lp then go rest ((a,b)::path)
else if a = lp then go rest ((b,a)::path)
else []
and go stones path = match stones with
| [] -> if left path = right path then [path] else []
| _ -> let open List.Monad_infix in choose_from stones >>= attach_to path
let chain_non_empty (first: dominoe) (rest: dominoe list): (dominoe list) option =
listToOption @@ go rest [first]
let chain = function
| [] -> Some []
| first::rest -> chain_non_empty first rest
Version data entries
101 entries across 101 versions & 1 rubygems