%% Problem %% --------------------- %% Take the number 192 and multiply it by each of 1, 2, and 3: %% %% 192 x 1 = 192 %% 192 x 2 = 384 %% 192 x 3 = 576 %% %% By concatenating each product we get the 1 to 9 pandigital, 192384576. %% We will call 192384576 the concatenated product of 192 and (1,2,3) %% %% The same can be achieved by starting with 9 and multiplying by 1, 2, 3, %% 4, and 5, giving the pandigital, 918273645, which is the concatenated %% product of 9 and (1,2,3,4,5). %% %% What is the largest 1 to 9 pandigital 9-digit number that can be formed %% as the concatenated product of an integer with (1,2, ... , n) where n 1? %% --------------------- -module(p038). -export([solve/0]). -include_lib("eunit/include/eunit.hrl"). solve() -> [ {N,M,multiply_concat(N,M)} || N <- lists:seq(9,10000), M <- lists:seq(1,8), is_pandigital(N,M) ]. is_pandigital(N, M) -> is_pandigital(multiply_concat(N, M)). multiply_concat(N, M) -> lists:flatten([ integer_to_list(N*X) || X <- lists:seq(1,M) ]). is_pandigital(String) -> lists:sort(String) == "123456789". is_pandigital_string_test() -> ?assertEqual(true, is_pandigital("918273645")). is_pandigital_number_test() -> ?assertEqual(true, is_pandigital(192, 3)).