in Swi prolog Given the following graph of possible flights between seven US cit

Question

in Swi prolog

Given the following graph of possible flights between seven US cities::   

Define a predicate route /33 that takes two cities as arguments and finds the routes to get from city A to a city B.. Your predicate should have the signature route((ccityA,, cityB,, Route)) .

Examples::

? - route((sseattle,, boston,, X))..

X = [sseattle,, omaha,, atlanta,, boston]] ;

false..

? - route(( fresno,, atlanta,, X))..

X = [ffresno,, seattle,, omaha,, atlanta]] ;

X = [ffresno,, albany,, seattle,, omaha,, atlanta]] ;

X = [ffresno,, albany,, dallas,, seattle,, omaha,, atlanta]] ;

false..

? - route((aalbany,, atlanta,, X))..

X = [aalbany,, seattle,, omaha,, atlanta]] ;

X = [aalbany,, dallas,, seattle,, omaha,, atlanta]] ;

false..

? - route((bboston,, atlanta,, X))..

false..   

Explanation / Answer

path(fresno,seattle).
path(fresno,albany).
path(fresno,boston).
path(seattle,omaha).
path(seattle,dallas).
path(omaha,albany).
path(omaha,atlanta).
path(albany,seattle).
path(albany,dallas).
path(atlanta,boston).
path(atlanta,dallas).
path(atlanta,albany).
path(dallas,seattle).
path(dallas,albany).

route(A,B,Route) :- direction(A,B,[A],Q), reverse(Q,Route).

direction(A,B,P,[B|P]) :- path(A,B).

direction(A,B,Visited,Route) :- path(A,C), C == B, +member(C,Visited), direction(C,B,[C|Visited],Route).

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