#!/usr/bin/env python
# encoding=utf-8 (pep 0263)

from linked_lists import LinkedList, Cons, Nil, member, member_anyX

def path(a, z, graph):
    for cesta, cena in path1(a, LinkedList([z]), 0, graph, 1):
        yield (cesta, cena)

def path1(a, akumulator_cesty, akumulator_ceny, graph, depth):
    if akumulator_cesty.head == a:
        yield (akumulator_cesty, akumulator_ceny)
    else:
        y = akumulator_cesty.head
        for x, cenaXY in adjacent_anyXcenaXY(y, graph):
            if not member(x, akumulator_cesty):
                for cesta, cena in path1(a, Cons(x, akumulator_cesty),
                                         akumulator_ceny + cenaXY, graph, depth+1):
                    yield (cesta, cena)

def adjacent_anyXcenaXY(y, edges):
    for a, b, cenaAB in member_anyX(edges):
        if y == a:
            yield (b, cenaAB)
        if y == b:
            yield (a, cenaAB)

# demonstracni vypis
if __name__ == "__main__":
    print('Cesta v grafu\n')
    cesta_, cena_ = next(path("s", "u", LinkedList([
        ("s", "t", 3), ("t", "v", 1), ("t", "u", 5), ("u", "t", 2), ("v", "u", 2)])))
    print('Cesta=%s' % cesta_)
    print('Cena=%d\n' % cena_)

Cesta v grafu

Cesta=['s', 't', 'u']
Cena=8

% nacteni:
/* ['2.9.2_22.pl']. */

path(A,Z,Graf,Cesta,Cena) :- path1(A,[Z],0,Graf,Cesta,Cena).

path1(A,[A|Cesta1],Cena1,_,[A|Cesta1],Cena1).
path1(A,[Y|Cesta1],Cena1,Graf,Cesta,Cena) :- adjacent(X,Y,CenaXY,Graf),
    \+ member(X,Cesta1),Cena2 is Cena1+CenaXY,
    path1(A,[X,Y|Cesta1],Cena2,Graf,Cesta,Cena).
    
adjacent(X,Y,CenaXY,Graf) :- member(X-Y/CenaXY,Graf);member(Y-X/CenaXY,Graf).

start:- 
    write('Cesta v grafu'),nl, nl,
    path(s, u, [s-t/3, t-v/1, t-u/5, u-t/2, v-u/2], Cesta, Cena),
    write('Cesta='), write(Cesta), nl,
    write('Cena='), write(Cena), nl, nl.

?-start.

Cesta v grafu

Cesta=[s,t,u]
Cena=8