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Less fun, but more reliable possibly, is the
mess-them-around-randomly-until-it-looks-right option.

It does this very stupidly, and will run indefinitely if you feed it
something for which there is no solution. (If you're really unlucky it
will run indefinitely if you feed it something really simple!)

- Peter

#!/usr/bin/env ruby

class Person
attr_reader :sname, :email
def initialize(details)
@fname, @sname, @email = details.scan(/(\w+)\s+(\w+)\s+<(.*)>/)[0]
end
def to_s() @fname + " " + @sname end
end

a, b = [], []

STDIN.each do |l|
someone = Person.new(l)
a << someone; b << someone
end

puts "Mixing..."

passes = 0
begin
ok = true
a.each_index do |idx|
passes += 1
if a[idx].sname == b[idx].sname
ok = false
r = rand(b.length); b[idx], b[r] = b[r], b[idx]
end
end
end until ok

a.each_index { |idx| puts "#{a[idx]} is santa'd with #{b[idx]}" }

puts "[#{passes} passes required.]"