compress-string.rb

#####################################
# Main implementation
#####################################
def compress(string)
  return "" if string.empty?

  result = ""
  cur_char = nil
  count = 0

  string.chars.each do |char|
    cur_char ||= char
    if cur_char == char
      count += 1
    else
      result << "#{count}#{cur_char}"
      cur_char = char
      count = 1
    end
  end

  result << "#{count}#{cur_char}"
end

#####################################
# Helpers
#####################################
def verify(expected, base)
  result = compress(base)

  puts "pass=#{expected == result}, expected=#{expected}, result=#{result}, base=#{base}"
end

#####################################
# Tests
#####################################
verify("4a", "aaaa")

verify("", "")

verify("4a1b2c", "aaaabcc")