Given a string of digits, output all the contiguous substrings of length n
in
that string in the order that they appear.
For example, the string "49142" has the following 3-digit series:
And the following 4-digit series:
And if you ask for a 6-digit series from a 5-digit string, you deserve whatever you get.
Note that these series are only required to occupy adjacent positions in the input; the digits need not be numerically consecutive.
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.
A subset of the Problem 8 at Project Euler http://projecteuler.net/problem=8
It's possible to submit an incomplete solution so you can see how others have completed the exercise.
defmodule StringSeriesTest do
use ExUnit.Case
# @tag :pending
test "slices of size 1" do
assert StringSeries.slices("01234", 1) == ["0", "1", "2", "3", "4"]
end
@tag :pending
test "slices of size 2" do
assert StringSeries.slices("01234", 2) == ["01", "12", "23", "34"]
end
@tag :pending
test "slices of size 3" do
assert StringSeries.slices("01234", 3) == ["012", "123", "234"]
end
@tag :pending
test "slices of size 4" do
assert StringSeries.slices("01234", 4) == ["0123", "1234"]
end
@tag :pending
test "slices same size as string" do
assert StringSeries.slices("01234", 5) == ["01234"]
end
@tag :pending
test "Unicode characters count as a single character" do
assert StringSeries.slices("José", 1) == ["J", "o", "s", "é"]
assert StringSeries.slices("José", 2) == ["Jo", "os", "sé"]
end
@tag :pending
test "slices with size longer than string return empty list" do
assert StringSeries.slices("01234", 6) == []
end
@tag :pending
test "slices with size zero or negative return empty list" do
assert StringSeries.slices("01234", -1) == []
assert StringSeries.slices("01234", 0) == []
end
end
ExUnit.start()
ExUnit.configure(exclude: :pending, trace: true)
defmodule StringSeries do
@doc """
Given a string `s` and a positive integer `size`, return all substrings
of that size. If `size` is greater than the length of `s`, or less than 1,
return an empty list.
"""
@spec slices(s :: String.t(), size :: integer) :: list(String.t())
def slices(_s, size) when size <= 0, do: []
def slices(s, size) do
s
|> String.split("", trim: true)
|> Enum.chunk_every(size, 1, :discard)
|> Enum.map(&Enum.join/1)
end
end
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