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Encode and de-code run-length encoding in Prolog with a single predicate.
encode([], []).
encode(XS, [E|ES]) :-
reverse(XS, XSReversed),
append(XRightReversed, XLeft, XSReversed),
XLeft \= [],
expand(XLeft, E),
reverse(XRightReversed, XRight),
encode(XRight, ES).
expand([X|XT], [Count, X]) :- expand(XT, [SubCount, X]), succ(SubCount, Count).
expand([], [0, _]).
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