39348
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(* ========================================================================= *)
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(* A HEAP DATATYPE FOR ML *)
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39444
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(* Copyright (c) 2001 Joe Hurd, distributed under the BSD License *)
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39348
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(* ========================================================================= *)
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structure Heap :> Heap =
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struct
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(* Leftist heaps as in Purely Functional Data Structures, by Chris Okasaki *)
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datatype 'a node = E | T of int * 'a * 'a node * 'a node;
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datatype 'a heap = Heap of ('a * 'a -> order) * int * 'a node;
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fun rank E = 0
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| rank (T (r,_,_,_)) = r;
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fun makeT (x,a,b) =
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if rank a >= rank b then T (rank b + 1, x, a, b) else T (rank a + 1, x, b, a);
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fun merge cmp =
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let
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fun mrg (h,E) = h
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| mrg (E,h) = h
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| mrg (h1 as T (_,x,a1,b1), h2 as T (_,y,a2,b2)) =
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case cmp (x,y) of
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GREATER => makeT (y, a2, mrg (h1,b2))
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| _ => makeT (x, a1, mrg (b1,h2))
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in
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mrg
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end;
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fun new cmp = Heap (cmp,0,E);
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fun add (Heap (f,n,a)) x = Heap (f, n + 1, merge f (T (1,x,E,E), a));
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fun size (Heap (_, n, _)) = n;
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fun null h = size h = 0;
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fun top (Heap (_,_,E)) = raise Empty
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| top (Heap (_, _, T (_,x,_,_))) = x;
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fun remove (Heap (_,_,E)) = raise Empty
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| remove (Heap (f, n, T (_,x,a,b))) = (x, Heap (f, n - 1, merge f (a,b)));
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fun app f =
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let
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fun ap [] = ()
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| ap (E :: rest) = ap rest
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| ap (T (_,d,a,b) :: rest) = (f d; ap (a :: b :: rest))
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in
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fn Heap (_,_,a) => ap [a]
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end;
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fun toList h =
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if null h then []
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else
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let
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val (x,h) = remove h
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in
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x :: toList h
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end;
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fun toStream h =
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if null h then Stream.Nil
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else
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let
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val (x,h) = remove h
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in
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Stream.Cons (x, fn () => toStream h)
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end;
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fun toString h =
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"Heap[" ^ (if null h then "" else Int.toString (size h)) ^ "]";
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end
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