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**412**- (**download**) (**annotate**)*Fri Sep 3 00:25:03 1999 UTC*(19 years, 10 months ago) by*monnier*File size: 1728 byte(s)

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(* * References that can be merged * * -- Allen *) signature UNION_FIND_REF = sig type 'a uref val uref : 'a -> 'a uref val !! : 'a uref -> 'a val ::= : 'a uref * 'a -> unit val == : 'a uref * 'a uref -> bool val eq : 'a uref * 'a uref -> bool val find : 'a uref -> 'a uref val union : ('a * 'a -> 'a) -> 'a uref * 'a uref -> bool val union' : 'a uref * 'a uref -> bool end structure UnionFindRef :> UNION_FIND_REF = struct datatype 'a uptree = ROOT of 'a * int | LINK of 'a uref withtype 'a uref = 'a uptree ref fun uref x = ref(ROOT(x,1)) fun eq (x : 'a uref,y : 'a uref) = x = y fun find r = let fun look (r as ref(ROOT _)) = r | look (r' as ref(LINK r)) = let val r'' = look r in if r <> r'' then r' := LINK r'' else (); r'' end in look r end fun == (x,y) = find x = find y fun !! r = let val ROOT(x,_) = !(find r) in x end fun ::=(r,x) = let val r as ref(ROOT(_,w)) = find r in r := ROOT(x,w) end fun union f (x,y) = let val r as ref(x as ROOT(i,w)) = find x val r' as ref(y as ROOT(j,w')) = find y in if r = r' then false else if w > w' then (r := ROOT(f(i,j),w+w'); r' := LINK r; true) else (r' := ROOT(f(i,j),w+w'); r := LINK r'; true) end fun union' (x,y) = let val r as ref(x as ROOT(i,w)) = find x val r' as ref(y as ROOT(j,w')) = find y in if r = r' then false else if w > w' then (r := ROOT(i,w+w'); r' := LINK r; true) else (r' := ROOT(j,w+w'); r := LINK r'; true) end end

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