Exactly one pair in the Prolog list

Question

Does anyone know how I can determine / verify that there is exactly one duplicate item in the break list?

I am studying a test.

0

user1895814 15 oct. 13 at 6:37 am

2 answers

one_duplicate(L) :-
    sort(L, Sorted),
    length(L, Len),
    length(Sorted, SortedLen),
    Len =:= SortedLen + 1.

-2

Active shawon 02 Apr 18 at 14:13

user1812457 · Accepted Answer · 2013-10-15T07:02:06+0000

Sorting the list with sort/2

. It removes duplicates, so if the sorted list is exactly one short, you have exactly one pair.

one_duplicate(L) :-
    sort(L, Sorted),
    length(L, Len),
    length(Sorted, SortedLen),
    Len =:= SortedLen + 1.

Finding a double pair is another question.