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unless Array.method_defined? :permutation
require 'backports/tools/arguments'
require 'enumerator'
class Array
def permutation(num = Backports::Undefined)
return to_enum(:permutation, num) unless block_given?
num = num.equal?(Backports::Undefined) ?
size :
Backports.coerce_to_int(num)
return self unless (0..size).include? num
final_lambda = lambda do |partial, remain|
yield partial
end
outer_lambda = (1..num).inject(final_lambda) do |proc, _|
lambda do |partial, remain|
remain.each_with_index do |val, i|
new_remain = remain.dup
new_remain.delete_at(i)
proc.call(partial.dup << val, new_remain)
end
end
end
outer_lambda.call([], dup)
end
end
end
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