subset coding exercise

Gemfile

# frozen_string_literal: true

source 'https://rubygems.org'

gem 'rspec'

subset.rb

# frozen_string_literal: true

# do all the needles exist in the haystack?
# allowing for multiple instances of elements in the needles where needles
# and haystacks are arrays of comparable objects
def subset?(needles, haystack)
  return false unless needles.length > 0 && haystack.length > 0

  haystacks = counter(haystack)
  counter(needles).each_pair do |key, value|
    return false unless haystacks.key?(key) && haystacks[key] >= value
  end
  true
end

# returns a hash with the original array elements as keys and the count of
# those elements in the array as values
def counter(elements)
  counts = {}
  elements.each do |e|
    counts[e] = counts.include?(e) ? counts[e] + 1 : 1
  end
  counts
end

subset_spec.rb

# frozen_string_literal: true

require_relative '../subset'

describe 'subset?' do
  let(:a) { ['l','m','n','o'] }
  let(:b) { ['n','o'] }
  let(:c) { [] }
  let(:d) { ['a','b','b','z'] }
  let(:e) { ['a','b','b','z','z'] }

  context 'there are more elements in needles than haystack' do
    subject { subset?(a,b) }
    it { is_expected.to be false }
  end

  context 'needles is an empty collection' do
    subject { subset?(c,b) }
    it { is_expected.to be false }
  end

  context 'haystack is an empty collection' do
    subject { subset?(a,c) }
    it { is_expected.to be false }
  end

  context 'needles are not in haystack' do
    subject { subset?(a,c) }
    it { is_expected.to be false }
  end

  context 'needles are in haystack' do
    subject { subset?(b,a) }
    it { is_expected.to be true }
  end

  context 'needles are in haystack, with multiple instances of some needles' do
    subject { subset?(d,e) }
    it { is_expected.to be true }
  end

end