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49 lines
1.5 KiB
49 lines
1.5 KiB
defmodule RomanNumerals do |
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@letters [ |
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%{:unitary => "I", :halfway => "V", :next => "X"}, |
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%{:unitary => "X", :halfway => "L", :next => "C"}, |
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%{:unitary => "C", :halfway => "D", :next => "M"}, |
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%{:unitary => "M", :halfway => "" , :next => ""} |
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] |
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@doc """ |
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Convert the number to a roman number. |
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""" |
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@spec numeral(pos_integer) :: String.t() |
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def numeral(number) do |
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numeral(number, @letters) |
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end |
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defp numeral(0, _letters) do |
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"" |
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end |
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defp numeral(number, [current | next]) do |
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next_iteration = Integer.floor_div(number, 10) |
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lower_part = number - (next_iteration * 10) |
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numeral(next_iteration, next) <> letter(lower_part, current) |
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end |
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defp letter(single_value, map) do |
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case single_value do |
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0 -> "" |
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1 -> String.duplicate(map[:unitary], 1) |
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2 -> String.duplicate(map[:unitary], 2) |
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3 -> String.duplicate(map[:unitary], 3) |
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4 -> map[:unitary] <> map[:halfway] |
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5 -> map[:halfway] |
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6 -> map[:halfway] <> String.duplicate(map[:unitary], 1) |
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7 -> map[:halfway] <> String.duplicate(map[:unitary], 2) |
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8 -> map[:halfway] <> String.duplicate(map[:unitary], 3) |
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9 -> map[:unitary] <> map[:next] |
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# OR... |
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# x when x == 0 -> "" |
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# x when x >= 1 and x <= 3 -> String.duplicate(map[:unitary], x) |
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# x when x == 4 -> map[:unitary] <> map[:halfway] |
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# x when x == 5 -> map[:halfway] |
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# x when x > 5 and x <= 8 -> map[:halfway] <> String.duplicate(map[:unitary], x - 5) |
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# _ -> map[:unitary] <> map[:next] |
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end |
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end |
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end
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