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BIN-DICT.SML
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1996-12-09
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(* binary-dict.sml
*
* COPYRIGHT (c) 1993 by AT&T Bell Laboratories. See COPYRIGHT file for details.
*
* This code was adapted from Stephen Adams' binary tree implementation
* of applicative integer sets.
*
* Copyright 1992 Stephen Adams.
*
* This software may be used freely provided that:
* 1. This copyright notice is attached to any copy, derived work,
* or work including all or part of this software.
* 2. Any derived work must contain a prominent notice stating that
* it has been altered from the original.
*
*
* Name(s): Stephen Adams.
* Department, Institution: Electronics & Computer Science,
* University of Southampton
* Address: Electronics & Computer Science
* University of Southampton
* Southampton SO9 5NH
* Great Britian
* E-mail: sra@ecs.soton.ac.uk
*
* Comments:
*
* 1. The implementation is based on Binary search trees of Bounded
* Balance, similar to Nievergelt & Reingold, SIAM J. Computing
* 2(1), March 1973. The main advantage of these trees is that
* they keep the size of the tree in the node, giving a constant
* time size operation.
*
* 2. The bounded balance criterion is simpler than N&R's alpha.
* Simply, one subtree must not have more than `weight' times as
* many elements as the opposite subtree. Rebalancing is
* guaranteed to reinstate the criterion for weight>2.23, but
* the occasional incorrect behaviour for weight=2 is not
* detrimental to performance.
*
*)
functor BinaryDict (K : ORD_KEY) : DICT =
struct
structure Key = K
open LibBase K
exception NotFound
(*
** val weight = 3
** fun wt i = weight * i
*)
fun wt (i : int) = i + i + i
datatype 'a dict =
E
| T of {
key : ord_key,
value : 'a,
cnt : int,
left : 'a dict,
right : 'a dict
}
fun numItems E = 0
| numItems (T{cnt,...}) = cnt
local
fun N(k,v,E,E) = T{key=k,value=v,cnt=1,left=E,right=E}
| N(k,v,E,r as T n) = T{key=k,value=v,cnt=1+(#cnt n),left=E,right=r}
| N(k,v,l as T n,E) = T{key=k,value=v,cnt=1+(#cnt n),left=l,right=E}
| N(k,v,l as T n,r as T n') =
T{key=k,value=v,cnt=1+(#cnt n)+(#cnt n'),left=l,right=r}
fun single_L (a,av,x,T{key=b,value=bv,left=y,right=z,...}) =
N(b,bv,N(a,av,x,y),z)
| single_L _ = raise Match
fun single_R (b,bv,T{key=a,value=av,left=x,right=y,...},z) =
N(a,av,x,N(b,bv,y,z))
| single_R _ = raise Match
fun double_L (a,av,w,T{key=c,value=cv,left=T{key=b,value=bv,left=x,right=y,...},right=z,...}) =
N(b,bv,N(a,av,w,x),N(c,cv,y,z))
| double_L _ = raise Match
fun double_R (c,cv,T{key=a,value=av,left=w,right=T{key=b,value=bv,left=x,right=y,...},...},z) =
N(b,bv,N(a,av,w,x),N(c,cv,y,z))
| double_R _ = raise Match
fun T' (k,v,E,E) = T{key=k,value=v,cnt=1,left=E,right=E}
| T' (k,v,E,r as T{right=E,left=E,...}) =
T{key=k,value=v,cnt=2,left=E,right=r}
| T' (k,v,l as T{right=E,left=E,...},E) =
T{key=k,value=v,cnt=2,left=l,right=E}
| T' (p as (_,_,E,T{left=T _,right=E,...})) = double_L p
| T' (p as (_,_,T{left=E,right=T _,...},E)) = double_R p
(* these cases almost never happen with small weight*)
| T' (p as (_,_,E,T{left=T{cnt=ln,...},right=T{cnt=rn,...},...})) =
if ln < rn then single_L p else double_L p
| T' (p as (_,_,T{left=T{cnt=ln,...},right=T{cnt=rn,...},...},E)) =
if ln > rn then single_R p else double_R p
| T' (p as (_,_,E,T{left=E,...})) = single_L p
| T' (p as (_,_,T{right=E,...},E)) = single_R p
| T' (p as (k,v,l as T{cnt=ln,left=ll,right=lr,...},
r as T{cnt=rn,left=rl,right=rr,...})) =
if rn >= wt ln then (*right is too big*)
let val rln = numItems rl
val rrn = numItems rr
in
if rln < rrn then single_L p else double_L p
end
else if ln >= wt rn then (*left is too big*)
let val lln = numItems ll
val lrn = numItems lr
in
if lrn < lln then single_R p else double_R p
end
else T{key=k,value=v,cnt=ln+rn+1,left=l,right=r}
local
fun min (T{left=E,key,value,...}) = (key,value)
| min (T{left,...}) = min left
| min _ = raise Match
fun delmin (T{left=E,right,...}) = right
| delmin (T{key,value,left,right,...}) = T'(key,value,delmin left,right)
| delmin _ = raise Match
in
fun delete' (E,r) = r
| delete' (l,E) = l
| delete' (l,r) = let val (mink,minv) = min r in
T'(mink,minv,l,delmin r)
end
end
in
fun mkDict () = E
fun insert (E,x,v) = T{key=x,value=v,cnt=1,left=E,right=E}
| insert (T(set as {key,left,right,value,...}),x,v) =
case cmpKey (key,x) of
Greater => T'(key,value,insert(left,x,v),right)
| Less => T'(key,value,left,insert(right,x,v))
| _ => T{key=x,value=v,left=left,right=right,cnt= #cnt set}
fun find (set, x) = let
fun mem E = raise NotFound
| mem (T(n as {key,left,right,...})) =
case cmpKey (x,key) of
Greater => mem right
| Less => mem left
| _ => #value n
in mem set end
fun peek arg = (SOME(find arg)) handle NotFound => NONE
fun remove (E,x) = raise NotFound
| remove (set as T{key,left,right,value,...},x) = (
case cmpKey (key,x)
of Greater => let
val (left', v) = remove(left, x)
in
(T'(key, value, left', right), v)
end
| Less => let
val (right', v) = remove (right, x)
in
(T'(key, value, left, right'), v)
end
| _ => (delete'(left,right),value)
(* end case *))
fun listItems d = let
fun d2l (E, l) = l
| d2l (T{key,value,left,right,...}, l) =
d2l(left,(key,value)::(d2l(right,l)))
in d2l (d,[]) end
fun revapp f d = let
fun a E = ()
| a (T{key,value,left,right,...}) = (a right; f(key,value); a left)
in a d end
fun app f d = let
fun a E = ()
| a (T{key,value,left,right,...}) = (a left; f(key,value); a right)
in a d end
fun fold f d init = let
fun a (E,v) = v
| a (T{key,value,left,right,...},v) = a(left,f(key,value,a(right,v)))
in a (d, init) end
fun revfold f d init = let
fun a (E,v) = v
| a (T{key,value,left,right,...},v) = a(right,f(key,value,a(left,v)))
in a (d, init) end
fun map f d = let
fun a E = E
| a (T{key,value,left,right,cnt}) = let
val left' = a left
val value' = f(key,value)
in
T{cnt=cnt, key=key,value=value',left = left', right = a right}
end
in a d end
fun transform f d = let
fun a E = E
| a (T{key,value,left,right,cnt}) = let
val left' = a left
val value' = f value
in
T{cnt=cnt, key=key,value=value',left = left', right = a right}
end
in a d end
end
end