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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 heap implementation, adapted from CLR *)
open StdLabels
open MoreLabels
(* Adapted from CLR *)
type ('key,'data) heap_el = { key: 'key;
data: 'data;
}
type ('key,'data) heap = { mutable a: ('key,'data) heap_el option array;
mutable length: int;
minsize: int;
cmp: 'key -> 'key -> bool;
}
let length heap = heap.length
let true_length heap = Array.length heap.a
(***************************************************************)
let parent i = (i-1)/2
let left i = 2 * i + 1
let right i = 2 * i + 2
let get heap i = match heap.a.(i) with
None -> raise (Failure "Heap.get: Attempt to examine None")
| Some el -> el
let exchange heap i j =
let temp = heap.a.(i) in
heap.a.(i) <- heap.a.(j);
heap.a.(j) <- temp
(***************************************************************)
let resize heap =
if heap.length > Array.length heap.a
then heap.a <-
Array.init ((Array.length heap.a) * 2)
~f:(fun i ->
if i < (Array.length heap.a)
then heap.a.(i)
else None)
else
if heap.length <= (Array.length heap.a)/3
&& (Array.length heap.a)/2 >= heap.minsize
then heap.a <-
Array.init ((Array.length heap.a)/ 2) ~f:(fun i -> heap.a.(i))
(***************************************************************)
let rec heapify heap i =
let left = left i in
let right = right i in
let largest =
if left < heap.length &&
heap.cmp (get heap left).key (get heap i).key
then left else i in
let largest =
if right < heap.length &&
heap.cmp (get heap right).key (get heap largest).key
then right
else largest
in
if i <> largest then
begin
exchange heap i largest;
heapify heap largest
end
(***************************************************************)
let build_heap_from_array cmp array length =
let heap = { a = array;
length = length;
minsize = length;
cmp = cmp
}
in
let rec loop i =
heapify heap i;
loop (i-1)
in
loop (parent length)
(***************************************************************)
let top heap = match heap.length with
0 -> raise Not_found
| _ -> let max = get heap 0 in
(max.key, max.data)
(***************************************************************)
let rec pop heap = match heap.length with
0 -> raise Not_found;
| _ -> let max = (get heap 0) in
heap.a.(0) <- heap.a.(heap.length - 1);
heap.length <- (heap.length - 1);
heapify heap 0;
resize heap;
(max.key, max.data)
(***************************************************************)
let push heap ~key ~data =
heap.length <- (heap.length + 1);
resize heap;
let rec loop i =
if i > 0 && heap.cmp key (get heap (parent i)).key then
begin
heap.a.(i) <- heap.a.(parent i);
loop (parent i)
end
else i
in
let i = loop (heap.length - 1) in
heap.a.(i) <- Some { key = key; data = data; }
(***************************************************************)
let empty cmp i =
{ a = Array.create i None;
length = 0;
minsize = i;
cmp = cmp;
}
|
