There are 10 types of people in the world: Those who understand binary, and those who don't.
You and your fellow cohort of those in the "know" when it comes to binary decide to come up with a secret "handshake".
1 = wink
10 = double blink
100 = close your eyes
1000 = jump
10000 = Reverse the order of the operations in the secret handshake.
Given a decimal number, convert it to the appropriate sequence of events for a secret handshake.
Here's a couple of examples:
Given the input 3, the function would return the array ["wink", "double blink"] because 3 is 11 in binary.
Given the input 19, the function would return the array ["double blink", "wink"] because 19 is 10011 in binary. Notice that the addition of 16 (10000 in binary) has caused the array to be reversed.
use Bitwise (or div/rem)
If you use Bitwise, an easy way to see if a particular bit is set is to compare
the binary AND (&&&
) of a set of bits with the particular bit pattern you
want to check, and determine if the result is the same as the pattern you're
checking.
Example:
Flags: 0b11011 Check: 0b11010
Flags &&& Check: 0b11010 (All checked bits are set)
Another:
Flags: 0b11011 Check: 0b10110
Flags &&& Check: 0b10010 (Third bit not set)
Execute the tests with:
$ elixir secret_handshake_test.exs
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
For more detailed information about the Elixir track, please see the help page.
Bert, in Mary Poppins http://www.imdb.com/title/tt0058331/quotes/qt0437047
It's possible to submit an incomplete solution so you can see how others have completed the exercise.
if !System.get_env("EXERCISM_TEST_EXAMPLES") do
Code.load_file("secret_handshake.exs", __DIR__)
end
ExUnit.start()
ExUnit.configure(trace: true, exclude: :pending)
defmodule SecretHandshakeTest do
use ExUnit.Case
describe "Create a handshake for a number" do
# @tag :pending
test "wink for 1" do
assert SecretHandshake.commands(1) == ["wink"]
end
@tag :pending
test "double blink for 10" do
assert SecretHandshake.commands(2) == ["double blink"]
end
@tag :pending
test "close your eyes for 100" do
assert SecretHandshake.commands(4) == ["close your eyes"]
end
@tag :pending
test "jump for 1000" do
assert SecretHandshake.commands(8) == ["jump"]
end
@tag :pending
test "combine two actions" do
assert SecretHandshake.commands(3) == ["wink", "double blink"]
end
@tag :pending
test "reverse two actions" do
assert SecretHandshake.commands(19) == ["double blink", "wink"]
end
@tag :pending
test "reversing one action gives the same action" do
assert SecretHandshake.commands(24) == ["jump"]
end
@tag :pending
test "reversing no actions still gives no actions" do
assert SecretHandshake.commands(16) == []
end
@tag :pending
test "all possible actions" do
assert SecretHandshake.commands(15) == ["wink", "double blink", "close your eyes", "jump"]
end
@tag :pending
test "reverse all possible actions" do
assert SecretHandshake.commands(31) == ["jump", "close your eyes", "double blink", "wink"]
end
@tag :pending
test "do nothing for zero" do
assert SecretHandshake.commands(0) == []
end
@tag :pending
test "do nothing if lower 5 bits not set" do
assert SecretHandshake.commands(32) == []
end
end
end
defmodule SecretHandshake do
@doc """
Determine the actions of a secret handshake based on the binary
representation of the given `code`.
If the following bits are set, include the corresponding action in your list
of commands, in order from lowest to highest.
1 = wink
10 = double blink
100 = close your eyes
1000 = jump
10000 = Reverse the order of the operations in the secret handshake
"""
@spec commands(code :: integer) :: list(String.t())
def commands(code) when code <= 0 or code >= 32,
do: []
def commands(code) when code >= 16 and code <= 31,
do: (code - 16) |> commands() |> Enum.reverse()
def commands(code) do
code
|> to_binary()
|> to_secrets()
end
defp to_binary(code, base \\ 2) do
code
|> :erlang.integer_to_binary(base)
|> String.pad_leading(base * 2, "0")
end
defp to_secrets(<<b0::8, b1::8, b2::8, b3::8>>) do
[{b0, "jump"}, {b1, "close your eyes"}, {b2, "double blink"}, {b3, "wink"}]
|> Enum.reduce([], fn
{49, secret}, acc -> [secret | acc]
{48, _}, acc -> acc
end)
end
end
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