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module DidYouMean
module Levenshtein # :nodoc:
# This code is based directly on the Text gem implementation
# Copyright (c) 2006-2013 Paul Battley, Michael Neumann, Tim Fletcher.
#
# Returns a value representing the "cost" of transforming str1 into str2
def distance(str1, str2)
n = str1.length
m = str2.length
return m if n.zero?
return n if m.zero?
d = (0..m).to_a
x = nil
# to avoid duplicating an enumerable object, create it outside of the loop
str2_codepoints = str2.codepoints
str1.each_codepoint.with_index(1) do |char1, i|
j = 0
while j < m
cost = (char1 == str2_codepoints[j]) ? 0 : 1
x = min3(
d[j+1] + 1, # insertion
i + 1, # deletion
d[j] + cost # substitution
)
d[j] = i
i = x
j += 1
end
d[m] = x
end
x
end
module_function :distance
private
# detects the minimum value out of three arguments. This method is
# faster than `[a, b, c].min` and puts less GC pressure.
# See https://github.com/ruby/did_you_mean/pull/1 for a performance
# benchmark.
def min3(a, b, c)
if a < b && a < c
a
elsif b < c
b
else
c
end
end
module_function :min3
end
end
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