I am new to prolog and I am trying to solve the following question. I am having difficulty trying to understand the logic to solve the problem. I know its similar to zebra problem but, I am unsure how to approach. Any help would be greatly appreciated.
The answers submitted by five students to a T/F quiz are as follows.
Teresa: T T F T F
Tim: F T T T F
Tania: T F T T F
Tom: F T T F T
Tony: T F T F T
Write a Prolog program quiz(Answer)
that asserts Answer is the list of t
and f
constants that is the correct answer to the quiz..
If you use SWI-Prolog, you can use library clpfd to solve the puzzle :, I get only one solution (f,f,t,f,t).
You have a solution [A,B,C,D,E]. You initialize the possibles solutions with
[A,B,C,D,E] ins 0..1,
You reify all the answers for teresa for example
teresea([1,1,0,1,0]).
A #= 1 #<==> TA
B #= 1 #<==> TB
.....
you compute the sum of Tis
sum([TA, TB, ...], #= , Steresa),
and later you will have for Tania got more answers right than Teresa did.
Stania #> Steresa
You get the solution with
label([A,B,C,D,E]).
Hope this helps
small puzzles like this can be solved by generate-and-test
solve(L) :-
% generator
length(L, 5), maplist(tf, L),
% Tania got more answers right than Teresa did.
matches(L, tania, Tania),
matches(L, teresa, Teresa), Tania > Teresa,
...
tf(t).
tf(f).
teresa(t, t, f, t, f).
tim(f, t, t, t, f).
...
Of course, matches(L, tania, Tania)
counts correct Tania' answers.
But, I don't find a solution. The only tuple that 'get thru' Tony, it's its exact result. So, this condition
Tony did not get all the answers right
cannot be solved...
edit I had a bug in matches/3. Of course there is a solution.
edit well, the CLP(FD) version can be very compact, while being more general...
teresa(t, t, f, t, f).
...
matches(L, P, N) :-
call(P, A,B,C,D,E),
foldl(eqsum, [A,B,C,D,E], L, 0, N).
eqsum(t,Ls,Acc,N) :- N #= Acc + (° #<==> Ls #= 1).
eqsum(f,Ls,Acc,N) :- N #= Acc + (° #<==> Ls #= 0).
solve(L) :-
length(°L, 5) ins 0..1,
% Tania got more answers right than Teresa did.
matches(L, tania, °) #> matches(L, teresa, °),
% Tom got more right than Tim.
matches(L, tom, °) #> matches(L, tim, °),
% Tony did not get all the answers right, nor did he get them all wrong.
matches(L, tony, °Tony) #> 0, Tony #< 5.
I used my lifter here.
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