CODEWITHSUNDEEP
prologsublist
Yasmine Mustafa
Yasmine Mustafa

Reputation: 11

Can someone help me with the Sublist Predicate (Prolog)?

I want to implement a predicate sublist1(I1,I2,L,Sub) that takes list L and returns Sub that includes elements of L from index I1 to index I2. My code gives me false all the time . Any Idea what's wrong?

sublist1(0,0,[H|T],[H|Sub]).


sublist1(I1,I2,[H|T],Sub):-
   I1 =0, I2>=I1,
   I is I2-1,
   sublist1(I1,I,T,[H|Sub]).

sublist1(I1,I2,[H|T],_):-
  I1>0, I2>I1,
  II1 is I1-1,
  II2 is I2-1,
  sublist1(II1,II2,T,_).

Upvotes: 1

Views: 94

Answers (1)

Rafalon
Rafalon

Reputation: 4515

Algorithmically, I would say this should work :

% sublist from 0 to 0 should return [H] for any List
sublist1(0,0,[H|T],[H]).

% sublist from 0 to n should return the first element followed with the sublist from 0 to n-1 of the tail
sublist1(I1,I2,[H|T],[H|Sub]):-
    I1 is 0, I2 > 0,
    II2 is I2 - 1,
    sublist1(I1,II2,T,Sub).

% sublist of [H|T] from I1 to I2 should return the sublist from I1-1 to I2-1 of T
sublist1(I1,I2,[H|T],Sub):-
  I1>0, I2>I1,
  II1 is I1-1,
  II2 is I2-1,
  sublist1(II1,II2,T,Sub).

Edit

Try it online (run execute and write sublist1(2,5,[0,1,2,3,4,5,6,7,8],S). for example). Use alt+91 for [ and alt+93 for ]

Upvotes: 1

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