my attempt at https://gist.github.com/knaveofdiamonds/7155189

jason_spec.rb

require 'rspec/autorun'

def get_results(string, s_i, chars, c_i )
  finds = []
  while i = string.index(chars[c_i], s_i)
    if chars[c_i + 1]
      if more_finds = get_results(string, i + 1, chars , c_i + 1)
        finds += more_finds.map{|a| a.unshift(i)}
      else
        return nil
      end
    else
      finds << [i]
    end
    s_i = i + 1
  end
  return finds
end

def letters(a, b)
  return get_results(a, 0, b.split(//), 0 )
end


describe "letters" do
  let(:a) { "hello world" }

  specify "example 1" do
    letters(a, "e").should == [[1]]
  end

  specify "example 2" do
    letters(a, "l").should == [[2],[3],[9]]
  end

  specify "example 3" do
    letters(a, "el").should == [[1,2], [1,3], [1,9]]
  end

  specify "example 4" do
    letters(a, "lo").should == [[2,4], [2,7], [3,4], [3,7]]
  end

  specify "example 5" do
    letters(a, "lod").should ==  [ [2,4,10], [2,7,10], [3,4,10], [3,7,10] ]
  end
end