#Yours truly has invited five of his colleagues to share a Christmas lunch 
#with him around the circular dinner table in his kitchen. Unfortunately, 
#two of the colleagues are not on speaking terms with each other, so they 
#cannot be seated together. In how many ways can we be seated around the table?


perms = []
keep = []
reject = []

#Circular Permutations = (N - 1)!
#perms = 12345.to_s.chars.to_a.permutation.map(&:join)

#Using alternate method
perms = 123456.to_s.chars.to_a.permutation.map(&:join)


for i in perms
  if i.to_s =~ /12/ then reject.push(i.to_s); next; end
  if i.to_s =~ /21/ then reject.push(i.to_s); next; end
  #alternate method needs following two lines
  if i.to_s =~ /^1.*2$/ then reject.push(i.to_s); next; end
  if i.to_s =~ /^2.*1$/ then reject.push(i.to_s); next; end
  keep.push(i.to_s)
end

puts "Total perms: #{perms.uniq.count}"
puts "Keep:         #{keep.uniq.count}"
puts "Reject:       #{reject.uniq.count}"

#Output for first method:
#Total perms: 120
#Keep:         72
#Reject:       48

puts keep.uniq.inspect
puts keep.uniq.size
puts
puts
puts reject.uniq.inspect

#alternate method
keep2 = []
for i in keep
  if i.to_s =~ /^6/ then keep2.push(i.to_s); next; end
end

puts "keep2.count: #{keep2.count}" #Output: 72
puts keep2.inspect