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|
(************************************************************************)
(* This file is part of SKS. SKS is free software; you can
redistribute it and/or modify it under the terms of the GNU General
Public License as published by the Free Software Foundation; either
version 2 of the License, or (at your option) any later version.
This program 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
General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program; 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 *)
open StdLabels
open MoreLabels
module Unix=UnixLabels
(** push and top are O(1).
pop and take are O(1) amortized.
to_list and length are O(n).
*)
(* Invariant:
if queue is not empty, outlist is not empty
queue.length = List.length(queue.outlist) + List.length(queue.inlist)*)
exception Empty
type 'a t = { inlist: 'a list;
outlist: 'a list;
length: int;
}
(*****************************************)
(*
let test_invariants queue =
assert
begin
queue.length = (List.length queue.outlist) + (List.length queue.inlist)
end;
assert
begin
(queue.length = 0) || List.length queue.outlist > 0
end
*)
let empty = { inlist = [];
outlist = [];
length = 0;
}
(*****************************************)
let push el queue =
if queue.outlist = [] then
let outlist = List.rev (el::queue.inlist)
in { inlist = [];
outlist = outlist;
length = queue.length + 1;
}
else
{ inlist = el::queue.inlist;
outlist = queue.outlist;
length = queue.length + 1;
}
let enq = push
(*****************************************)
let top queue =
match queue.outlist with
[] -> (if queue.inlist != []
then failwith "FQueue.top: BUG. inlist should be empty but isn't"
else raise Empty)
| hd::tl -> hd
(*****************************************)
let pop queue = match queue.outlist with
hd::[] -> (hd, { inlist = [];
outlist = (List.rev queue.inlist);
length = queue.length - 1})
| hd::tl -> (hd, { inlist = queue.inlist;
outlist = tl;
length = queue.length - 1;})
| [] ->
if queue.inlist = []
then raise Empty
else (match List.rev queue.inlist with
[] -> failwith "FQueue.top: BUG. inlist should not be empty here"
| hd::tl -> (hd, { inlist=[];
outlist=tl;
length = queue.length - 1;
}))
(*****************************************)
let discard queue =
let (el,new_q) = pop queue in
new_q
let deq = pop
(*****************************************)
let to_list queue =
queue.inlist @ (List.rev (queue.outlist))
(*****************************************)
let length queue = queue.length
let is_empty queue = queue.length = 0
|
