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Update the levenshtein distance method in guides.
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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 | ||
# This code is based directly on the Text gem implementation | ||
# Returns a value representing the "cost" of transforming str1 into str2 | ||
def self.distance str1, str2 | ||
s = str1 | ||
t = str2 | ||
n = s.length | ||
m = t.length | ||
max = n/2 | ||
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# matrix initialization | ||
d = [] | ||
0.upto(m) { |i| d << [i] } | ||
0.upto(n) { |j| d[0][j] = j } | ||
return m if (0 == n) | ||
return n if (0 == m) | ||
return n if (n - m).abs > max | ||
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# 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 | ||
d = (0..m).to_a | ||
x = nil | ||
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str1.each_char.each_with_index do |char1,i| | ||
e = i+1 | ||
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str2.each_char.each_with_index do |char2,j| | ||
cost = (char1 == char2) ? 0 : 1 | ||
x = [ | ||
d[j+1] + 1, # insertion | ||
e + 1, # deletion | ||
d[j] + cost # substitution | ||
].min | ||
d[j] = e | ||
e = x | ||
end | ||
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d[m] = x | ||
end | ||
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# all done | ||
return d[m][n] | ||
return x | ||
end | ||
end | ||
end |