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prolog

Print an Eulerian path of graph

I am completely new to Prolog, but I have to do this for a homework. At the entry is given a undirected coherent graph. Write a program in Prolog, which prints euler circle of this graph. Thanks for answers. For example i have this edge:

edge(a,b).
edge(b,e).
edge(a,c).
edge(c,d).
edge(e,d).
Solution

  • This is an Eulerian path ; not necessarily a circle.

    eulerpath(E, Cs) :-
   setof(A-B, call(E, A,B), ABs),
   edges_path(ABs, Cs).

edges_path([], [_]).
edges_path(ABs0, [X,Y|Xs]) :-
    select(A-B,ABs0,ABs),
    ( A = X, B = Y ; B = X, A = Y ),
    edges_path(ABs, [Y|Xs]).
  
?- eulerpath(edge, Cs).
   Cs = [a,b,e,d,c,a]
;  Cs = [b,a,c,d,e,b]
;  Cs = [a,c,d,e,b,a]
;  Cs = [c,a,b,e,d,c]
;  Cs = [b,e,d,c,a,b]
;  Cs = [e,b,a,c,d,e]
;  Cs = [c,d,e,b,a,c]
;  Cs = [d,c,a,b,e,d]
;  Cs = [e,d,c,a,b,e]
;  Cs = [d,e,b,a,c,d]
;  false.