ocaml-containers/multiSet.ml

(*
copyright (c) 2013, simon cruanes
all rights reserved.

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modification, are permitted provided that the following conditions are met:

redistributions of source code must retain the above copyright notice, this
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this software is provided by the copyright holders and contributors "as is" and
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*)

(** {1 Multiset} *)

module type S = sig
  type elt
  type t

  val empty : t

  val is_empty : t -> bool

  val mem : t -> elt -> bool

  val count : t -> elt -> int

  val singleton : elt -> t

  val add : t -> elt -> t

  val remove : t -> elt -> t

  val min : t -> elt

  val max : t -> elt

  val union : t -> t -> t

  val intersection : t -> t -> t

  val diff : t -> t -> t

  val contains : t -> t -> bool

  val compare : t -> t -> int

  val equal : t -> t -> bool

  val cardinal : t -> int
    (** Number of distinct elements *)

  val iter : t -> (int -> elt -> unit) -> unit

  val fold : t -> 'b -> ('b -> int -> elt -> 'b) -> 'b

  val of_list : elt list -> t

  val to_list : t -> elt list
end

module Make(O : Set.OrderedType) = struct
  module M = Map.Make(O)

  type t = int M.t

  type elt = O.t

  let empty = M.empty

  let is_empty = M.is_empty

  let mem ms x = M.mem x ms

  let count ms x =
    try M.find x ms
    with Not_found -> 0

  let singleton x = M.singleton x 1

  let add ms x =
    let n = count ms x in
    M.add x (n+1) ms

  let remove ms x =
    let n = count ms x in
    match n with
    | 0 -> ms
    | 1 -> M.remove x ms
    | _ -> M.add x (n-1) ms

  let min ms =
    fst (M.min_binding ms)

  let max ms =
    fst (M.max_binding ms)

  let union m1 m2 =
    M.merge
      (fun x n1 n2 -> match n1, n2 with
        | None, None -> assert false
        | Some n1, None -> Some n1
        | None, Some n2 -> Some n2
        | Some n1, Some n2 -> Some (n1+n2))
      m1 m2

  let intersection m1 m2 =
    M.merge
      (fun x n1 n2 -> match n1, n2 with
        | None, None -> assert false
        | Some _, None
        | None, Some _ -> None
        | Some n1, Some n2 -> Some (Pervasives.min n1 n2))
      m1 m2

  let diff m1 m2 =
    M.merge
      (fun x n1 n2 -> match n1, n2 with
        | None, None -> assert false
        | Some n1, None -> Some n1
        | None, Some n2 -> None
        | Some n1, Some n2 ->
          if n1 > n2 
            then Some (n1 - n2)
            else None)
      m1 m2

  let contains m1 m2 =
    try 
      M.for_all (fun x c -> M.find x m1 >= c) m2
    with Not_found -> false
    
  let compare m1 m2 =
    M.compare (fun x y -> x - y) m1 m2

  let equal m1 m2 =
    M.equal (fun x y -> x = y) m1 m2

  let cardinal m = M.cardinal m

  let iter m f =
    M.iter (fun x n -> f n x) m

  let fold m acc f =
    M.fold (fun x n acc -> f acc n x) m acc

  let of_list l =
    let rec build acc l = match l with
    | [] -> acc
    | x::l' -> build (add acc x) l'
    in
    build empty l

  let to_list m =
    (* [n_cons n x l] is the result of applying [fun l -> x :: l]  [n] times
        to [l] *)
    let rec n_cons n x l = match n with
    | 0 -> l
    | 1 -> x::l
    | _ -> n_cons (n-1) x (x::l)
    in
    fold m [] (fun acc n x -> n_cons n x acc)
end