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Index finite lists of positive integers: Difference between revisions
Index finite lists of positive integers (view source)
Revision as of 02:42, 20 May 2014
, 10 years ago→{{header|Ruby}}: added Bijection
(→{{header|Python}}: correct when list begins with 0s) |
(→{{header|Ruby}}: added Bijection) |
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[1, 2, 3, 10, 100, 987654321]
</pre>
=== Bijection ===
{{trans|Python}}
<lang ruby>def unrank(n)
return [0] if n==1
n.to_s(2)[1..-1].split('0',-1).map(&:size)
end
def rank(x)
return 0 if x.empty?
('1' + x.map{ |a| '1'*a }.join('0')).to_i(2)
end
for x in 0..10
puts "%3d : %-18s: %d" % [x, a=unrank(x), rank(a)]
end
puts
x = [1, 2, 3, 5, 8]
puts "#{x} => #{rank(x)} => #{unrank(rank(x))}"</lang>
{{out}}
<pre>
0 : [] : 0
1 : [0] : 1
2 : [0, 0] : 2
3 : [1] : 3
4 : [0, 0, 0] : 4
5 : [0, 1] : 5
6 : [1, 0] : 6
7 : [2] : 7
8 : [0, 0, 0, 0] : 8
9 : [0, 0, 1] : 9
10 : [0, 1, 0] : 10
[1, 2, 3, 5, 8] => 14401279 => [1, 2, 3, 5, 8]
</pre>
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