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=={{header|Ruby}}==
{{works with|Ruby|1.8.7+}}
<lang ruby>p [1,2,3].permutation.to_a</lang>
{{out}}
[[1, 2, 3], [1, 3, 2], [2, 1, 3], [2, 3, 1], [3, 1, 2], [3, 2, 1]]
</pre>
However, this method will produce indistinct permutations if the array has indistinct elements. If you need to find all the permutations of an array of which many elements are the same, the method below will be more efficient.
<lang ruby>class Array
# Yields distinct permutations of _self_ to the block.
# This method requires that all array elements be Comparable.
def distinct_permutation # :yields: _ary_
# If no block, return an enumerator. Works with Ruby 1.8.7.
block_given? or return enum_for(:distinct_permutation)
copy = self.sort
yield copy.dup
return if size < 2
while true
# from: "The Art of Computer Programming" by Donald Knuth
j = size - 2;
j -= 1 while j > 0 && copy[j] >= copy[j+1]
if copy[j] < copy[j+1]
l = size - 1
l -= 1 while copy[j] >= copy[l]
copy[j] , copy[l] = copy[l] , copy[j]
copy[j+1..-1] = copy[j+1..-1].reverse
yield copy.dup
else
break
end
end
end
end
permutations = []
[1,1,2].distinct_permutation do |p| permutations << p end
p permutations
# => [[1, 1, 2], [1, 2, 1], [2, 1, 1]]
if RUBY_VERSION >= "1.8.7"
p [1,1,2].distinct_permutation.to_a
# => [[1, 1, 2], [1, 2, 1], [2, 1, 1]]
end</lang>
=={{header|Run BASIC}}==
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