it’s always interesting to see the different solutions and learn from each other
not sure using the String.replace or Regex.scan is efficient as you process the whole line, most of the processing is therefore useless
I opted to scan left to right and right to left with a pattern-matching function.
Although it’s more verbose, I think it’s more efficient as you stop processing a line asap.
def p2(file) do
file
|> File.read!()
|> String.split("\n")
|> Enum.map(fn line ->
ldigit(line) * 10 + rdigit(String.reverse(line))
end)
|> Enum.sum()
end
defp ldigit("one" <> _), do: 1
defp ldigit("two" <> _), do: 2
defp ldigit("three" <> _), do: 3
defp ldigit("four" <> _), do: 4
defp ldigit("five" <> _), do: 5
defp ldigit("six" <> _), do: 6
defp ldigit("seven" <> _), do: 7
defp ldigit("eight" <> _), do: 8
defp ldigit("nine" <> _), do: 9
defp ldigit("zero" <> _), do: 0
defp ldigit(<<c>> <> _) when c >= ?0 and c <= ?9, do: c - ?0
defp ldigit(<<_, s::binary>>), do: ldigit(s)
defp rdigit("eno" <> _), do: 1
defp rdigit("owt" <> _), do: 2
defp rdigit("eerht" <> _), do: 3
defp rdigit("ruof" <> _), do: 4
defp rdigit("evif" <> _), do: 5
defp rdigit("xis" <> _), do: 6
defp rdigit("neves" <> _), do: 7
defp rdigit("thgie" <> _), do: 8
defp rdigit("enin" <> _), do: 9
defp rdigit("orez" <> _), do: 0
defp rdigit(<<c>> <> _) when c >= ?0 and c <= ?9, do: c - ?0
defp rdigit(<<_, s::binary>>), do: rdigit(s)
