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From: eiverson@nmsu.edu (Eric Iverson)
Newsgroups: comp.lang.prolog
Subject: the great split up
Message-ID: <EIVERSON.90Feb11221732@hades.nmsu.edu>
Date: 12 Feb 90 05:17:32 GMT
Sender: news@nmsu.edu
Distribution: comp
Organization: NMSU Computer Science
Lines: 29


Here is a split routine I wrote.  Think of it as one string acting as
a catalyst to split another string in two.  If you can think of a
better, more efficient way to do it, please let me know.  This is for
Quintus Prolog and is going to be called many many times.


% split(Cat,String,A,B) binds Cat onto String and splits it into A and B.
% String is split at the center of Cat.
split([C|C1],[S|S1],[S|A],B):-
    C == S,split2(C1,S1,A,B,1,_);
    split([C|C1],S1,A,B).

split2([],X,[],X,N,H):-
    H is N-N//2,!.

split2([C|C1],[C|S1],A,B,N,H):-
    N1 is N+1,!,
    split2(C1,S1,A1,B1,N1,H),
    (N1 > H,B=[C|B1],A=A1,!;
     A=[C|A1],B=B1),!.

--
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