Convert a hexadecimal number, represented as a string (e.g. "10af8c"), to its decimal equivalent using first principles (i.e. no, you may not use built-in or external libraries to accomplish the conversion).
On the web we use hexadecimal to represent colors, e.g. green: 008000, teal: 008080, navy: 000080).
The program should handle invalid hexadecimal strings.
Execute the tests with:
$ mix test
In the test suites, all but the first test have been skipped.
Once you get a test passing, you can unskip the next one by
commenting out the relevant @tag :pending
with a #
symbol.
For example:
# @tag :pending
test "shouting" do
assert Bob.hey("WATCH OUT!") == "Whoa, chill out!"
end
Or, you can enable all the tests by commenting out the
ExUnit.configure
line in the test suite.
# ExUnit.configure exclude: :pending, trace: true
If you're stuck on something, it may help to look at some of the available resources out there where answers might be found.
All of Computer Science http://www.wolframalpha.com/examples/NumberBases.html
It's possible to submit an incomplete solution so you can see how others have completed the exercise.
defmodule HexadecimalTest do
use ExUnit.Case
test "returns 1 when hex is 1" do
assert Hexadecimal.to_decimal("1") == 1
end
@tag :pending
test "returns 12 when hex is c" do
assert Hexadecimal.to_decimal("c") == 12
end
@tag :pending
test "hexadecimal is case insensitive" do
assert Hexadecimal.to_decimal("C") == 12
end
@tag :pending
test "returns 16 when hex is 10" do
assert Hexadecimal.to_decimal("10") == 16
end
@tag :pending
test "returns 175 when hex is af" do
assert Hexadecimal.to_decimal("af") == 175
end
@tag :pending
test "returns 256 when hex is 100" do
assert Hexadecimal.to_decimal("100") == 256
end
@tag :pending
test "returns 105_166 when hex is 19ace" do
assert Hexadecimal.to_decimal("19ace") == 105_166
end
@tag :pending
test "returns 0 when hex is invalid" do
assert Hexadecimal.to_decimal("carrot") == 0
end
@tag :pending
test "returns 0 when hex represents black" do
assert Hexadecimal.to_decimal("000000") == 0
end
@tag :pending
test "returns 16_777_215 when hex represents white" do
assert Hexadecimal.to_decimal("ffffff") == 16_777_215
end
@tag :pending
test "returns 16_776_960 when hex represents yellow" do
assert Hexadecimal.to_decimal("ffff00") == 16_776_960
end
end
ExUnit.start()
ExUnit.configure(exclude: :pending, trace: true)
defmodule Hexadecimal do
@hex_alphabet %{
"a" => 10, "A" => 10, "b" => 11, "B" => 11, "c" => 12, "C" => 12,
"d" => 13, "D" => 13, "e" => 14, "E" => 14, "f" => 15, "F" => 15,
}
@spec to_decimal(binary) :: integer
def to_decimal(hex) do
if Regex.match?(~r/^[a-fA-F0-9]*$/, hex), do: from_hex(hex), else: 0
end
defp from_hex(""), do: 0
defp from_hex(<<char::binary-size(1), rest::binary>> = hex) do
from_hex(rest) + (to_integer(char) * pow(String.length(hex) - 1))
end
defp to_integer(char) do
if char in Map.keys(@hex_alphabet), do: @hex_alphabet[char], else: String.to_integer(char)
end
defp pow(exp, base \\ 16), do: base |> :math.pow(exp) |> round()
end
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