Pallindromes

pallindrome.rb

class String

  def pallindrome?
    string = self.downcase.gsub(/[^0-9a-z]/i,'')
    return false if string.length <= 1
    string.reverse == string
  end

  def collect_possible_starts_and_end
    #{ a: [0, 1], b: [3], c: [1,4,6]}
    return  if @pallindrome_char_instances if @pallindrome_char_instances
    @pallindrome_char_instances = {}
    for i in (0..self.length-1)
      if @pallindrome_char_instances.has_key?(self[i])
        @pallindrome_char_instances[self[i]] << i
      else
        @pallindrome_char_instances[self[i]] = [i]
      end
    end
    @pallindrome_char_instances
  end

  def find_pallindromes
    possibles = collect_possible_starts_and_end

    pallindromes =[]
    for key in possibles.keys
      indexes = possibles[key]
      if indexes.length > 1
        for start_i in indexes
          for end_i in indexes
            pallindromes << self[start_i..end_i] unless !self[start_i..end_i].pallindrome?
          end
        end
      end
    end
    pallindromes
  end

  def extract_pallindrome
    find_pallindromes.last
  end
end

pallindrome_spec.rb

require "rspec"
require_relative "pallindrome"

describe "#pallindrome?" do
  context "when given a string containing a pallindrome" do
    it "returns true when it is a pallindrome" do
      expect("aba".pallindrome?).to be(true)
      expect("moom".pallindrome?).to be true
      expect("qamoomaq".pallindrome?).to be true
      expect("qamoaomaq".pallindrome?).to be true
      expect("civic".pallindrome?).to be true
      expect("cdr".pallindrome?).to be false
    end


    it "allows mixed case pallindromes" do
      expect("QAmoaomAq".pallindrome?).to be true
      expect("qaMOAOMaQ".pallindrome?).to be true
    end

    it "ignores whitespace" do
      expect("A slut nixes sex in Tulsa".pallindrome?).to be true
    end

    it "ignores punctuation" do
      expect("A car, a man, a maraca.".pallindrome?).to be true
      expect("Cigar? Toss it in a can. It is so tragic.".pallindrome?).to be true
    end

    it "it should be case insensititve" do
      expect("Aba".pallindrome?).to be(true)
    end

    it "should not care about non-alphanumerics" do
      expect("a b, a".pallindrome?).to be(true)
    end
  end

  context "with a string that is not a pallindrome" do
    it "returns false" do
     expect("cdr".pallindrome?).to eq(false)
     expect("".pallindrome?).to be false
     expect(".?.".pallindrome?).to be false
     expect(".i.".pallindrome?).to be false
     expect(".iaI.".pallindrome?).to be true
   end
 end
end

describe "#find_pallindromes" do
  context "with a string containing at least one pallindrome" do
    it "should find pallindromes in a sentence" do
      expect("aba hello".find_pallindromes).to include("aba")
    end

    it "should find pallindromes in a sentence" do
      expect("aba hello".find_pallindromes).to include("aba")
    end

    it "extracts pallindromes from a string" do
      expect("a moom".find_pallindromes).to eq ['moom', 'oo']
      expect("aba Cain: a maniac.".find_pallindromes).to eq ["aba", "a Ca", "ain: a mania", "a ma", "in: a mani", "n: a man"]
      expect("a radar".find_pallindromes).to eq ["a ra", "ada", "radar"]
      expect("aba hello".find_pallindromes).to eq ["aba", "ll"]
      expect("Amy, must I jujitsu my ma?".find_pallindromes).to eq ["my, m", "my, must I jujitsu my m", "must I jujitsu m", "my m", "y, must I jujitsu my", "ust I jujitsu", "st I jujits", "t I jujit", "juj"]
    end

    it "should return an empty array when no pallindromes are present" do
      expect("no palies".find_pallindromes.length).to eq(0)
    end
  end
end