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paulfioravanti's solution

to Gigasecond in the Elixir Track

Published at Jun 19 2019 · 0 comments
Instructions
Test suite
Solution

Note:

This exercise has changed since this solution was written.

Calculate the moment when someone has lived for 10^9 seconds.

A gigasecond is 10^9 (1,000,000,000) seconds.

Running tests

Execute the tests with:

$ elixir gigasecond_test.exs

Pending tests

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.

Source

Chapter 9 in Chris Pine's online Learn to Program tutorial. http://pine.fm/LearnToProgram/?Chapter=09

Submitting Incomplete Solutions

It's possible to submit an incomplete solution so you can see how others have completed the exercise.

gigasecond_test.exs

if !System.get_env("EXERCISM_TEST_EXAMPLES") do
  Code.load_file("gigasecond.exs", __DIR__)
end

ExUnit.start()
ExUnit.configure(exclude: :pending, trace: true)

defmodule GigasecondTest do
  use ExUnit.Case

  # @tag :pending
  test "from 4/25/2011" do
    assert Gigasecond.from({{2011, 4, 25}, {0, 0, 0}}) == {{2043, 1, 1}, {1, 46, 40}}
  end

  @tag :pending
  test "from 6/13/1977" do
    assert Gigasecond.from({{1977, 6, 13}, {0, 0, 0}}) == {{2009, 2, 19}, {1, 46, 40}}
  end

  @tag :pending
  test "from 7/19/1959" do
    assert Gigasecond.from({{1959, 7, 19}, {0, 0, 0}}) == {{1991, 3, 27}, {1, 46, 40}}
  end

  @tag :pending
  test "yourself" do
    # customize these values for yourself
    # your_birthday = {{year1, month1, day1}, {0, 0, 0}}
    # assert Gigasecond.from(your_birthday) == {{year2, month2, day2}, {hours, minutes, seconds}}
  end
end
defmodule Gigasecond do
  @seconds :math.pow(10, 9)
           |> round()

  @doc """
  Calculate a date one billion seconds after an input date.
  """
  @spec from(
          {{pos_integer, pos_integer, pos_integer},
           {pos_integer, pos_integer, pos_integer}}
        ) ::
          :calendar.datetime()

  def from(erl_datetime) do
    erl_datetime
    |> NaiveDateTime.from_erl!()
    |> NaiveDateTime.add(@seconds)
    |> NaiveDateTime.to_erl()
  end
end

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