Convert string so that 0<->9, 1<->8, ..., and 4<->5.

each.rb

require 'benchmark'
# Convert string so that 0<->9, 1<->8, ..., and 4<->5.
# For example, from "8253593637" to "1746406362"

def use_each_char(input)
  input.each do |s|
    r = "0"*s.length
    s.each_char.with_index do |c,i|
      r[i] = (105 - c.ord).chr
    end
  end
end

def use_each_byte(input)
  input.each do |s|
    r = "0"*s.length
    s.each_byte.with_index do |c,i|
      r[i] = (105 - c).chr
    end
  end
end

def use_map_join(input)
  input.each do |s|
    r = s.each_byte.to_a.map{|v| (105 - v).chr}.join("")
  end
end

srand(1)
input = Array.new(100) do
  s = ""
  10000.times do
    s << (rand*10).to_i.to_s
  end
  s
end

r1 = Benchmark.realtime do 
  use_each_char(input)
end

r2 = Benchmark.realtime do 
  use_each_byte(input)
end

r3 = Benchmark.realtime do 
  use_map_join(input)
end

puts "each_char #{r1} [sec]" # => each_char 0.8496029999805614 [sec]
puts "each_byte #{r2} [sec]" # => each_byte 0.7626579999923706 [sec]
puts "map_join  #{r3} [sec]" # => map_join  0.2027799999341368 [sec]