Mercurial > repos > other > SevenLanguagesInSevenWeeks
changeset 63:e159ec90a072
Day 2 self-study, with insert sort
| author | IBBoard <dev@ibboard.co.uk> |
|---|---|
| date | Sat, 30 Sep 2017 14:26:58 +0100 |
| parents | 96e77f914f9b |
| children | f6fce6a54e94 |
| files | 3-Prolog/day2-self-study.pl |
| diffstat | 1 files changed, 26 insertions(+), 0 deletions(-) [+] |
line wrap: on
line diff
--- /dev/null Thu Jan 01 00:00:00 1970 +0000 +++ b/3-Prolog/day2-self-study.pl Sat Sep 30 14:26:58 2017 +0100 @@ -0,0 +1,26 @@ +% Skipping Towers of Hanoi - need to think how to map it to rules when it is about movement. +% +% Reversing a list +reverse_list([], []). +reverse_list([Head], Reversed) :- Reversed = [Head]. +reverse_list([Head1|Tail], Reversed) :- reverse_list(Tail, ReversedTail), append(ReversedTail,[Head1], Reversed). + +% Finding the smallest element +% Remember: Prolog evaluates both sides, so a rule with "Head > Holder" first only happens if +% that statement is true! +find_smallest([], Smallest, Smallest). +find_smallest([Head|Tail], Holder, Smallest) :- Head > Holder, find_smallest(Tail, Holder, Smallest). +find_smallest([Head|Tail], Holder, Smallest) :- Head =< Holder, find_smallest(Tail, Head, Smallest). +% And give the user a sensible version that doesn't need them to supply an arbitrary (potentially wrong) +% initial value +find_smallest([Head|Tail], Smallest) :- find_smallest([Head|Tail], Head, Smallest). + +% Sort a list +insert_sort([], [], []). +insert_sort([Head], [], [Head]). +insert_sort([], Sorted, Sorted). +insert_sort([UHead|UTail], [], Result) :- insert_sort(UTail, [UHead], Result). +insert_sort([UHead|UTail], [SHead|STail], Result) :- UHead > SHead, insert_sort([UHead], STail, NewSTail), insert_sort(UTail, [SHead|NewSTail], Result). +insert_sort([UHead|UTail], [SHead|STail], Result) :- UHead =< SHead, insert_sort(UTail, [UHead|[SHead|STail]], Result). +% Friendly user version +insert_sort([UHead|UTail], Result) :- insert_sort([UHead|UTail], [], Result). \ No newline at end of file