gistfile1.rb

require 'rspec/autorun'

def get_indexes(needle, haystack)
  (0...haystack.length).find_all { |i| haystack[i,1] == needle }
end

def map_indexes(needle, haystack)
  needle.split('').map do |nee|
    get_indexes nee, haystack
  end
end

def letters(haystack, needle)
  indexes = map_indexes(needle, haystack)
  first_index = indexes.shift
  first_index.product(*indexes).select{|match| match == match.sort}
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