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defmodule Concatenation do
def iter([]) do
nil
end
def iter([o]) do
{o, []}
end
def iter([f | t]) do
with [l | t] <- Enum.reverse(t) do
{String.to_integer("#{f}#{l}"), Enum.reverse(t)}
end
end
def value(ints) do
ints
|> Stream.unfold(&iter/1)
|> Enum.sum()
end
end
ExUnit.start()
defmodule ConcatenationTest do
use ExUnit.Case
test "concatenation value" do
assert Concatenation.iter([6, 12, 25, 1]) == {61, [12, 25]}
assert Concatenation.iter([12, 25]) == {1225, []}
assert Concatenation.iter([]) == nil
assert Concatenation.value([6, 12, 25, 1]) == 1286
end
test "concatenation value more elems" do
assert Concatenation.iter([10, 7, 31, 5, 2, 2]) == {102, [7, 31, 5, 2]}
assert Concatenation.value([10, 7, 31, 5, 2, 2]) == 489
end
test "concatenation value odd elems" do
assert Concatenation.iter([1, 2, 10]) == {110, [2]}
assert Concatenation.iter([2]) == {2, []}
assert Concatenation.value([1, 2, 10]) == 112
end
end
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