CODEWITHSUNDEEP
prolog
misha182
misha182

Reputation: 13

create a list in prolog in range of two numbers

I want to build list of numbers that are in range of two given numbers.

For example: betweenRange(1,5,X)

will give the answer: X=[1,2,3,4,5].

any idea how to do that?

I've tried something like:

elementsBetween(N1, N2, [N1|_]):-
   N2 =:= N1.
elementsBetween(N1, N2, List):-
   N2 > N1, N2New is N2-1, 
   elementsBetween(N1, N2New, [N2|List]).

but its not working, some problem with backtracking after the recursion.

Upvotes: 1

Views: 3377

Answers (3)

Mateusz Piątkowski
Mateusz Piątkowski

Reputation: 51

Better yet, use numlist:

numlist(From, To, List).

Upvotes: 0

JanPro
JanPro

Reputation: 11

Here's a simple solution:

    betweenRange(Lo, Hi, Range) :- findall(N, between(Lo, Hi, N), Range).

It puts all Ns that satisfy between(Lo,Hi,N) into a list Range.

Upvotes: 1

Dennis Vash
Dennis Vash

Reputation: 53884

betweenToList(X,X,[X]) :- !.
betweenToList(X,Y,[X|Xs]) :-
    X =< Y,
    Z is X+1,
    betweenToList(Z,Y,Xs).

Output:

?- betweenToList(1,5,X).
X = [1, 2, 3, 4, 5].

?- betweenToList(1,2,X).
X = [1, 2].

?- betweenToList(1,8,X).
X = [1, 2, 3, 4, 5, 6, 7, 8].

?- betweenToList(1,1,X).
X = [1].

?- betweenToList(1,0,X).
false.

Same logic by decreasing Y you can use reverse/2 (Easy to implement):

betweenDecYAux(X,X,[X]) :- !.
betweenDecYAux(X,Y,[Y|Ys]) :-
    X =< Y,
    Z is Y-1,
    betweenDecYAux(X,Z,Ys).

betweenDecY(X,Y,R) :-
    betweenDecYAux(X,Y,L),
    reverse(L, R). % reverse [c,b,a] to [a,b,c]

Output:

?- betweenDecY(1,6,X).
X = [1, 2, 3, 4, 5, 6].

?- betweenDecY(2,8,X).
X = [2, 3, 4, 5, 6, 7, 8].

?- betweenDecY(1,0,X).
false.

Upvotes: 2

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