added example 6.3_14

6.3_14.pl

+% nacteni:
+/* ['6.3_14.pl']. */
+
+:- retractall(write_all_X/3).
+:- retractall(start/0).
+
+:- use_module(library(clpfd)). % clpq , clpr
+
+queens(N,L,Type):- length(L,N),
+                   L ins 1..N,
+                   constr_all(L),
+                   labeling(Type,L).
+constr_all([]).
+constr_all([X|Xs]):- constr_between(X,Xs,1), constr_all(Xs).
+constr_between(_,[],_).
+constr_between(X,[Y|Ys],N):- no_threat(X,Y,N),
+                             N1 is N+1,
+                             constr_between(X,Ys,N1).
+                             
+no_threat(X,Y,J):- X #\= Y, X+J #\= Y, X-J #\= Y.
+
+:- dynamic
+       write_all_X/3,
+       start/0.
+       
+write_all_X(Goal,X,Name):-
+            call(Goal),write('  '),write(Name),write(' = '),write(X),nl,fail.
+write_all_X(_,_,_).
+
+start:- 
+    write('CLP - Problem N dam'),nl,nl,
+    write('Vysledek dotazu "queens(4, L, [ff])":'),nl,
+    write_all_X(queens(4, L, [ff]), L, 'L').
+    
+?-start.

6.3_14.py

+#!/usr/bin/env python
+# encoding=utf-8 (pep 0263)
+
+# je zapotrebi nainstaloval balicek python-constraint
+from constraint import Problem
+from linked_lists import LinkedList, Nil
+
+def queens(n):
+    problem = Problem()
+    domain = range(n+1)[1:]
+    variables = LinkedList(list("X%d" % i for i in range(n+1)[1:]))
+    for name in variables:
+        problem.addVariable(name, domain)
+    constr_all(problem, variables)
+    return problem
+
+def constr_all(problem, variables):
+    if variables == Nil:
+        return
+    x = variables.head
+    xs = variables.tail
+    constr_between(problem, x, xs, 1)
+    constr_all(problem, xs)
+
+def constr_between(problem, x, other_variables, n):
+    if other_variables == Nil:
+        return
+    y = other_variables.head
+    ys = other_variables.tail
+    no_threat(problem, x, y, n)
+    constr_between(problem, x, ys, n + 1)
+
+def no_threat(problem, x, y, j):
+    problem.addConstraint(lambda x_, y_: x_ != y_ and x_ + j != y_ and x_ - j != y_, (x, y))
+
+# demonstracni vypis
+if __name__ == "__main__":
+    print("CLP - Problem N dam\n")
+
+    print("Vysledek volani queens(4).getSolutions():")
+    for solution in queens(4).getSolutions():
+        print(solution)

6.3_14.py.out

+CLP - Problem N dam
+
+Vysledek volani queens(4).getSolutions():
+{'X2': 1, 'X3': 4, 'X1': 3, 'X4': 2}
+{'X2': 4, 'X3': 1, 'X1': 2, 'X4': 3}