55 lines
1.3 KiB
Plaintext
55 lines
1.3 KiB
Plaintext
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/*************************************************************************
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* *
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* YAP Prolog *
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* *
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* Yap Prolog was developed at NCCUP - Universidade do Porto *
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* *
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* Copyright L.Damas, V.S.Costa and Universidade do Porto 1985-1997 *
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* *
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**************************************************************************
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* *
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* File: sort.pl *
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* Last rev: *
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* mods: *
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* comments: sorting in Prolog *
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* *
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*************************************************************************/
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/* The three sorting routines are all variations of merge-sort, done by
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bisecting the list, sorting the nearly equal halves, and merging the
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results. The half-lists aren't actually constructed, the number of
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elements is counted instead (which is why 'length' is in this file).
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*/
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% length of a list.
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length(L,M) :- var(M), !, '$$_length1'(L,0,M).
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length(L,M) :- '$$_length2'(M,L).
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'$$_length1'([], M, M).
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'$$_length1'([_|L], N, O) :-
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M is N + 1,
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'$$_length1'(L, M, O).
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'$$_length2'(N, L) :-
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( N =:= 0
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->
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L = []
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;
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L = [_|L1],
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N1 is N - 1,
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'$$_length2'(N1, L1)
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).
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sort(L,O) :-
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'$sort'(L,O).
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msort(L,O) :-
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'$msort'(L,O).
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keysort(L,O) :-
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'$keysort'(L,O).
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