count_letters.rb

def count_letters(str)
  letters = Hash.new{0}
  str = str.gsub(/\s+/, "") #removes spaces
  str.each_char { |c| letters[c] += 1 }
  puts letters.inspect
end

puts "What's your string?"
user_input = gets.chomp

count_letters(user_input)

# Return indices of each character

def indices_letters(str)
  letters = Hash.new(0)
  str.each_char.each_with_index do |c, i|
    if letters.has_key?(c)
      letters[c].push(i)
    else
      letters[c] = Array.new(0)
      letters[c].push(i)
    end
  end
  # removing spaces at this stage so that we return correct indices
  letters.delete(" ")
  puts letters.inspect
end

indices_letters(user_input)

# More elegant

def indices_letters_elegant(str)
  letters = Hash.new {|h,k| h[k] = [] } # we make sure we have an empty array at each key
  str.each_char.each_with_index {|c, i| letters[c].push(i)}
  letters.delete(" ")
  puts letters.inspect
end

indices_letters_elegant(user_input)