[英]Combing odd and even regular expression to regular grammar?
我有這個課我需要寫常規語法。 語法是{a,b,c},其中有一個奇數的a和c,但偶數個b。
良好字符串的示例:
壞字符串
甚至b的我的正則表達式是b∗(ab∗ab∗)∗b∗
(我不知道在哪里包括c)
我對奇數a的正則表達式是(c|a(b|c)*a)*a(b|c)*
我的奇數c的正則表達式是(c|a(b|c)*c)*c(b|c)*
我認為常規語法看起來像這樣:
s -> [a], a
s -> [c], c
a -> [a], a
a -> [b], b
a -> [c], c
b -> [b]
b -> [b], b
b -> [a], a
b -> [c], c
c -> [c], c
c -> [a], a
c -> [b], b
我覺得我很遺憾。 任何幫助表示贊賞!
這是SWI-Prolog中可能的解決方案:
:- use_module(library(clpfd)).
:- use_module(library(lambda)).
odd_even(Lst) :-
variables_signature(Lst, Sigs),
automaton(Sigs, _, Sigs,
% start in s, end in i
[source(s), sink(i)],
% if we meet 0, counter A of a is incremented of one modulo 2
% the others are unchanged
[arc(s, 0, s, [(A+1) mod 2, B, C]),
arc(s, 1, s, [A, (B+1)mod 2, C]),
arc(s, 2, s, [A, B, (C+1) mod 2]),
arc(s, 0, i, [(A+1) mod 2, B, C]),
arc(s, 1, i, [A, (B+1)mod 2, C]),
arc(s, 2, i, [A, B, (C+1) mod 2])],
% name of counters
[A, B, C],
% initial values of counters
[0, 0, 0],
% needed final values of counters
[1,0,1]).
% replace a with 0, b with 1, c with 2
variables_signature(Lst, Sigs) :-
maplist(\X^Y^(X = a -> Y = 0; (X = b -> Y = 1; Y = 2)), Lst, Sigs).
示例:
?- odd_even([a,c,c,a,c,c,a,c]).
true.
?- odd_even([a,c,c,a,c,c,a]).
false.
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