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31 lines
1 KiB
Erlang
31 lines
1 KiB
Erlang
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% Find the largest palindrome made from the product of two 3-digit numbers.
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% A palindromic number reads the same both ways. The largest palindrome made from the product of two 2-digit numbers is 9009 = 91 99.
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% Find the largest palindrome made from the product of two 3-digit numbers.
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-module(e004).
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-export([
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main/1
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]).
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product(Min, Max) ->
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product(Min, Max, Max, Max, 0).
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product(Min, _, N1, _, Product) when N1 < Min ->
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Product;
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product(Min, Max, N1, N2, Product) when N2 < Min ->
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product(Min, Max, N1 - 1, Max, Product);
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product(Min, Max, N1, N2, Product) ->
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P = trunc(N1 * N2),
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S = integer_to_list(trunc(N1 * N2)),
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R = lists:reverse(S),
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if
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S == R, P > Product ->
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product(Min, Max, N1, N2 - 1, P);
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true ->
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product(Min, Max, N1, N2 - 1, Product)
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end.
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main(_) ->
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io:format("Largest palindrome product of 2-digit numbers: ~w~n", [product(10, 99)]),
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io:format("Largest palindrome product of 3-digit numbers: ~w~n", [product(100, 999)]).
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