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module RailsGuides
module Levenshtein
# Based on the pseudocode in http://en.wikipedia.org/wiki/Levenshtein_distance
def self.distance(s1, s2)
s = s1.unpack('U*')
t = s2.unpack('U*')
m = s.length
n = t.length
# matrix initialization
d = []
0.upto(m) { |i| d << [i] }
0.upto(n) { |j| d[0][j] = j }
# distance computation
1.upto(m) do |i|
1.upto(n) do |j|
cost = s[i] == t[j] ? 0 : 1
d[i][j] = [
d[i-1][j] + 1, # deletion
d[i][j-1] + 1, # insertion
d[i-1][j-1] + cost, # substitution
].min
end
end
# all done
return d[m][n]
end
end
end
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