Write a predicate that returns the second to last element in a list.
# Prolog
Write a predicate that returns the second to last element in a list.
?- second last clement(x, [a.b.c.d,e]
x = d
?- second last element (X, [])
false.
?- second last element (3, [5,4,3,2,1])
true.
Homework Answers
There are many ways to return a second to last item in a
list.
1.
secondLast(L, X) :-
append(_, [X, _], L).
This predicate can get you the second last item in a list.
2.
secondLast([X,_], X).
secondLast([_|T], X) :- secondLast(T, X).
This predicate also gets you the second last item in a list.
Here the first statement (secondLast([X,_], X).) says x is an
element which is in a position of second to last in a list [X,_],
which is true. _ means the last item which we dont need.
The second statement (secondLast([_|T], X) :- secondLast(T, X).)
states that X is the second to last element of the list, T. This is
also true of any list that is 3 or more elements.
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Write a predicate that returns the second to last element in a list.
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