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March 13, 2024 17:17
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Superpermutation in Ruby
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# Naive implementation for finding the superpermutation of n symbols | |
# https://en.wikipedia.org/wiki/Superpermutation | |
n = 4 | |
permutations = (1..n).to_a.permutation.map{|a| a.join} | |
s = permutations.first | |
permutations.shift | |
while (permutations.length > 0) | |
idx = nil | |
nn = n | |
while (idx.nil? && nn > 1) | |
nn -= 1 | |
# Find the longest match for n - 1, n - 2 and so on | |
idx = permutations.index {|c| c[0..nn - 1] == s[-nn..-1]} | |
end | |
# Add the difference between the strings | |
s << permutations[idx][nn..n - 1] | |
permutations.delete_at(idx) | |
end | |
if n == 3 && s == "123121321" | |
puts "Correct for n = 3" | |
end | |
if n == 4 && s == "123412314231243121342132413214321" | |
puts "Correct for n = 4" | |
end | |
puts s | |
puts "Length #{s.length}" |
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