Number of times each character used in a string

gistfile1.rb

def count_chars(input_string)
  char_count_map = {}
  char_list = []
  
  input_string.chars.each do |ch|
    if not char_count_map.has_key?(ch)
      char_list << ch
      char_count_map[ch] = 0
    end
    char_count_map[ch] += 1
  end
  
  char_list.each do |c|
    puts "#{c}: (#{char_count_map[c]}) times."
  end
end