I was happy to see a problem today that didn’t take me hours to solve.
While I knew there was an equation to solve it in an instant, I didn’t bother to look it up and just iterated over the whole problem space.
I fully expected an order of magnitude that required the mathematical approach in part 2, but was surprised that my trivial approach just took 4 seconds to run on part 2.
(Using Erlang for the fun right now:)
a(In) ->
[T, D] = [parse(L) || L <- In],
G = [opt(Time, Dist) || {Time, Dist} <- lists:zip(T, D)],
lists:foldl(fun(X, Acc) -> X * Acc end, 1, G).
parse(L) -> [list_to_integer(I) || I <- tl(re:split(L, "\\s+", [trim, {return, list}]))].
opt(Time, Dist) -> length([1 || R <- lists:seq(1, Time), R * (Time - R) > Dist]).
b(In) ->
[T, D] = [list_to_integer(parse_join(L)) || L <- In],
opt(T, D).
parse_join(L) -> lists:concat([I || I <- tl(re:split(L, "\\s+", [trim, {return, list}]))]).
There might even be an off by 1 error in my code (> Dist or >= Dist?), but it still worked on both example an my input.
Probably I’ll clean it up and try to implement the efficient solution in the evening, thanks for the great explanation @Aetherus
