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|
(******************************************************************************
* Core *
* *
* Copyright (C) 2008- Jane Street Holding, LLC *
* Contact: opensource@janestreet.com *
* WWW: http://www.janestreet.com/ocaml *
* *
* *
* This library is free software; you can redistribute it and/or *
* modify it under the terms of the GNU Lesser General Public *
* License as published by the Free Software Foundation; either *
* version 2 of the License, or (at your option) any later version. *
* *
* This library is distributed in the hope that it will be useful, *
* but WITHOUT ANY WARRANTY; without even the implied warranty of *
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU *
* Lesser General Public License for more details. *
* *
* You should have received a copy of the GNU Lesser General Public *
* License along with this library; if not, write to the Free Software *
* Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA *
* *
******************************************************************************)
(** Simple implementation of a polymorphic functional queue *)
(** Performance guarantees:
- push, top, and bottom are O(1).
- pop is O(1) amortized.
- to_list is O(n).
- length is O(1).
*)
(** Invariants:
- iff queue is not empty, outlist is not empty
- iff queue has more than 1 element, then inlist is not empty
- queue.length = List.length queue.outlist + List.length queue.inlist
*)
open Std_internal
exception Empty with sexp
type 'a t = { inlist : 'a list; outlist : 'a list; length : int } with bin_io, sexp
let test_invariants queue =
let n_out = List.length queue.outlist in
let n_in = List.length queue.inlist in
assert (queue.length = n_out + n_in);
assert (queue.length = 0 || n_out <> 0);
assert (queue.length <= 1 || n_in <> 0)
let empty = { inlist = []; outlist = []; length = 0 }
let push el queue =
let inlist, outlist =
if queue.length = 0 then [], [el]
else el :: queue.inlist, queue.outlist
in
{ inlist = inlist; outlist = outlist; length = queue.length + 1 }
(** pushes el on the top of the queue, effectively making it
the least recently enqueued element *)
let push_top el queue =
let inlist, outlist =
if queue.inlist = [] then List.rev queue.outlist, [el]
else queue.inlist, el :: queue.outlist
in
{ inlist = inlist; outlist = outlist; length = queue.length + 1 }
(** same as push *)
let enq = push
(** returns bottom (most-recently enqueued) item *)
let bot_exn queue =
match queue.inlist, queue.outlist with
| [], [x] | x :: _, _ -> x
| [], [] -> raise Empty
| [], _ :: _ :: _ ->
raise (Bug "Fqueue.bot_exn: empty inlist and outlist with len > 1")
let bot queue = try Some (bot_exn queue) with Empty -> None
(** returns top (least-recently enqueued) item *)
let top_exn queue =
match queue.outlist with
| x :: _ -> x
| [] -> raise Empty
let top queue = try Some (top_exn queue) with Empty -> None
(** returns top of queue and queue with top removed *)
let pop_exn queue =
let x, inlist, outlist =
match queue.inlist, queue.outlist with
| [_] as inlist, [x] -> x, [], inlist
| y :: ytl, [x] -> x, [y], List.rev ytl
| inlist, x :: xtl -> x, inlist, xtl
| [], [] -> raise Empty
| _ :: _, [] -> raise (Bug "Fqueue.pop_exn: outlist empty, inlist not")
in
x, { inlist = inlist; outlist = outlist; length = queue.length - 1 }
let pop queue = try Some (pop_exn queue) with Empty -> None
(** same as pop *)
let deq = pop
let deq_exn = pop_exn
(** returns queue with top removed *)
let discard_exn queue = snd (pop_exn queue)
let to_list queue = List.append queue.outlist (List.rev queue.inlist)
let sexp_of_t sexp_of_a q = Sexplib.Conv.sexp_of_list sexp_of_a (to_list q)
let length queue = queue.length
let is_empty queue = queue.length = 0
|
