CODEWITHSUNDEEP
prologbacktrackingsudoku
Gagan Ganapathy
Gagan Ganapathy

Reputation: 67

Sudoku of alphabets solver in prolog

:- use_module(library(clpfd)).

go(Rows):- 
  foreach(J in 1..9, K in 1..9, Number = Rows[J,K], 
  Code is 0'A + Number - 1, char_code(Letter, Code), Rows[J,K] is Letter,nl)

sudoku(Rows) :-  
  append(Rows, Vs), Vs ins 1..9,
  maplist(all_distinct, Rows),
  transpose(Rows, Columns),     
  maplist(all_distinct, Columns),     
  Rows = [A,B,C,D,E,F,G,H,I],     
  blocks(A, B, C), 
  blocks(D, E, F), 
  blocks(G, H, I), 
  maplist(label, Rows),

blocks([], [], []).       
  blocks([A,B,C|Bs1], [D,E,F|Bs2], [G,H,I|Bs3]) :-     
  all_distinct([A,B,C,D,E,F,G,H,I]),      
  blocks(Bs1, Bs2, Bs3).

But this solves a sudoku containing numbers from 1 to 9 , I need to do something to convert the 1 to 9 into A to I

What I am thinking is to traverse each element in the grid and check the value accordingly replace it with the corresponding alphabet.

How can I traverse and replace the numbers or is there some better way to solve this?

Error :

enter image description here

Thanks! :D

Upvotes: 0

Views: 288

Answers (1)

Paulo Moura
Paulo Moura

Reputation: 18663

To convert the numbers in the 1..9 interval to letters in the A..I interval you can use the goal:

Code is 0'A + Number - 1, char_code(Letter, Code)

For example:

?- Number = 4, Code is 0'A + Number - 1, char_code(Letter, Code).
Number = 4,
Code = 68,
Letter = 'D'.

Assuming that the solution matrix is represented by a list of lists, the conversion can be accomplished using something like:

convert_matrix([], []).
convert_matrix([Row| Rows], [ConvertedRow| ConvertedRows]) :-
    convert_row(Row, ConvertedRow),
    convert_matrix(Rows, ConvertedRows).

convert_row([], []).
convert_row([Number| Numbers], [Letter| Letters]) :-
    Code is 0'A + Number - 1,
    char_code(Letter, Code),
    convert_row(Numbers, Letters).

But the conversion code can be simplified using maplist predicates. I leave that to you as an exercise. Hint: define an auxiliary predicate that takes a number and returns the corresponding letter.

Upvotes: 1

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