Re: determinism

Daniel Diaz wrote:
> michel levy a écrit :
> 
>>Could you help to write this program :
>>det(T,G) succeeds if and only if G succeeds once and only once and give
>>the T answer.
>>1) I don't want the solution below by findall, because I want to try at
>>most two back tracks on G.
>>det(T,G) :- findall(T,G,L),length(L,1)
>>
>>2) I know already call_det but it's not the solution because G can have
>>choice points, but only one answer.
>>
> 
> 
> You can do it using a global variable to count solutions. Stop when the
> second is reached.
> 
> 
> det(Goal) :-
> 	det1(Goal).
> 
> det(_) :-
> 	g_read(det_count, 1).
> 	
> 
> det1(Goal) :-
> 	g_assign(det_count, 0),
> 	call(Goal),
> 	g_inc(det_count, Count), % increment and return the counter
> 	Count = 2,	% cut if 2nd solution is reached (else fail)
> 	!,
> 	fail.
> 
> Hope this helps
> 
> 
Thank you really much for your help.
Your solution is very simple to understand.

I have modify it slightly to have the answer (like in findall).

det(Answer,Goal):-
	det1(Answer,Goal).

det(Answer,_) :-
	g_read(det_count, 1),retract(sol(Answer)).	

det1(Answer,Goal) :-
	g_assign(det_count, 0),
	call(Goal),assertz(sol(Answer)),
	g_inc(det_count, Count), % increment and return the counter
	Count = 2,	% cut if 2nd solution is reached (else fail)
	!,
	retract(sol(_)),
	fail.
I have modify it slightly to have the answer (like in findall).

My goal was to write a program :
sudoko(L) succeds if L is a 81 elements list of a sudoku
and fails if the answer is not unique.

Therefore now I write
L = [  _,_,_,1,3,_,_,_,7,
           5,7,_,6,_,_,_,_,_,
	  9,_,1,_,2,_,3,_,_,
	  _,4,_,_,_,_,2,_,_,
	  1,_,_,_,5,_,_,_,9,
	  2,_,_,_,4,6,_,_,1,
	  _,_,_,9,_,_,_,_,8,
	  _,6,_,_,7,_,_,_,_,
	  8,_,_,4,1,_,5,_,3],
det(L,sudoku(L)).
L = [6,2,4,1,3,5,9,8,7,
5,7,3,6,8,9,4,1,2,
9,8,1,7,2,4,3,5,6,
7,4,6,8,9,1,2,3,5,
1,3,8,2,5,7,6,4,9,
2,5,9,3,4,6,8,7,1,
4,1,5,9,6,3,7,2,8,
3,6,2,5,7,8,1,9,4,
8,9,7,4,1,2,5,6,3]
yes

L = [  _,_,_,_,3,_,_,_,7,
           5,7,_,6,_,_,_,_,_,
	  9,_,1,_,2,_,3,_,_,
	  _,4,_,_,_,_,2,_,_,
	  1,_,_,_,5,_,_,_,9,
	  2,_,_,_,4,6,_,_,1,
	  _,_,_,9,_,_,_,_,8,
	  _,6,_,_,7,_,_,_,_,
	  8,_,_,4,1,_,5,_,_],
det(L,sudoku(L)).
no
This sudoku problem has more than a solution.

My sudoku progam has a side effect, write the sudoku in a visible shape 
and why I get really in the last case is :

det(L,sudoku(L)).
[4,2,6][5,3,9][8,1,7]
[5,7,3][6,8,1][9,2,4]
[9,8,1][7,2,4][3,6,5]
---------------------
[6,4,7][1,9,8][2,5,3]
[1,3,8][2,5,7][6,4,9]
[2,5,9][3,4,6][7,8,1]
---------------------
[7,1,5][9,6,2][4,3,8]
[3,6,4][8,7,5][1,9,2]
[8,9,2][4,1,3][5,7,6]



[4,2,6][5,3,9][8,1,7]
[5,7,3][6,8,1][9,2,4]
[9,8,1][7,2,4][3,6,5]
---------------------
[6,4,8][1,9,7][2,5,3]
[1,3,7][2,5,8][6,4,9]
[2,5,9][3,4,6][7,8,1]
---------------------
[7,1,5][9,6,2][4,3,8]
[3,6,4][8,7,5][1,9,2]
[8,9,2][4,1,3][5,7,6]

(1 ms) no

So you see the first two solutions (there are plenty of solutions).

	Sincerely yours


-- 
Michel Levy
36 rue George Sand
38400 Saint Martin d'Heres