string_algorithms.rb

require 'rspec'

describe 'Inspector' do
  describe '.uniq?' do
    it 'works for a unique string' do
      expect(Inspector.uniq?('abc')).to be true
    end

    it 'works for a repeating string' do
      expect(Inspector.uniq?('abcabc')).to be false
    end
  end

  describe '.reverse' do
    it 'reverses strings' do
      expect(Inspector.reverse('foobar')).to eq 'raboof'
      expect(Inspector.reverse('hugo')).to eq 'oguh'
    end
  end

  describe '.permutations?' do
    it 'returns true for permutations' do
      expect(Inspector.permutations?('abc', 'cba')).to be true
      expect(Inspector.permutations?('foobar', 'barfoo')).to be true
    end

    it 'returns false for non-permutations' do
      expect(Inspector.permutations?('abcd', 'abc')).to be false
      expect(Inspector.permutations?('fbar', 'foobaz')).to be false
      expect(Inspector.permutations?('foo', 'foobaz')).to be false
    end

    it 'accounts for whitespace' do
      expect(Inspector.permutations?('abc ', 'abc')).to be false
    end
  end

  describe '.compress' do
    it 'compresses strings using the counts of repeated characters' do
      expect(Inspector.compress('aabcccccaaa')).to eq 'a2b1c5a3'
    end
  end
end


class Inspector
  class << self
    def uniq?(str)
      letters = {}
      str.each_char do |c|
        if letters[c].nil?
          letters[c] = true
        else
          return false
        end
      end

      true
    end

    def reverse(str)
      new_string = ''
      str.each_char { |c| new_string.prepend(c) }
      new_string
    end

    def reverse(str)
      mid_length = str.length / 2

      1.upto(mid_length) do |i|
        left_char = str[i - 1]
        right_char = str[-i]

        str[i - 1] = right_char
        str[-i] = left_char
      end
      str
    end

    def permutations?(string_a, string_b)
      string_a.split('').sort.join == string_b.split('').sort.join
    end

    def compress(str)
      output = ""

      char = str[0]
      count = 0
      str << " "

      str.each_char do |c|
        if char != c
          output << "#{char}#{count}"
          count = 1
          char = c
        else
          count += 1
        end
      end

      output
    end
  end
end