Created
May 18, 2020 18:06
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-module(week227). | |
-compile([export_all]). | |
-include_lib("eunit/include/eunit.hrl"). | |
join(Xs, Ys) -> | |
accumulate(shunt(Xs, []), Ys). | |
shunt([], Ys) -> | |
Ys; | |
shunt([X|Xs], Ys) -> | |
shunt(Xs, [X|Ys]). | |
accumulate([] ,Result) -> | |
Result; | |
accumulate([X|Xs], Result) -> | |
accumulate(Xs, [X|Result]). | |
concat([]) -> | |
[]; | |
concat([X|Xs]) -> | |
join(X,concat(Xs)). | |
member(_N, []) -> | |
false; | |
member(N, [X|Xs]) -> | |
case X =:= N of | |
true -> | |
true; | |
false -> | |
member(N, Xs) | |
end. | |
perms([]) -> | |
[[]]; | |
perms(L) -> | |
[[X|Y] || X <- L, Y <- perms(L--[X])]. | |
tests() -> | |
?assertEqual(join([],[]),[]), | |
?assertEqual(join([1,2,3],[4,5,6]),[1,2,3,4,5,6]), | |
?assertEqual(concat(["hello", "world"]),"helloworld"), | |
% ?assertEqual(concat([]), []), | |
?assertEqual(perms([]), [[]]), | |
?assertEqual(perms([1,2,3]), [[1,2,3],[1,3,2],[2,1,3],[2,3,1],[3,1,2],[3,2,1]]). |
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A few things to notice…
?assertEqual/2
… the expected result is the first argument. You will notice that in the output when the assertion fails.member/2
…2.5. Or you can use short-circuiting…
perms/1
works? I'll leave this here, just in case