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32 lines
771 B
Ruby
32 lines
771 B
Ruby
require "matrix"
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class MutableMatrix < Matrix
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public :"[]="
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end
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# Returns the edit distance between strings a and b
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# https://en.wikipedia.org/wiki/Edit_distance
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def edit_distance (a, b)
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# memo is the matrix for dynamic programming
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# memo[i, j] = the edit distance between the
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# prefixes of a and b of size i and j.
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memo = MutableMatrix.zero(a.size + 1, b.size + 1)
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a.size.times {|i| memo[i + 1, 0] = i + 1}
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b.size.times {|j| memo[0, j + 1] = j + 1}
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a.size.times do |i|
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b.size.times do |j|
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if a[i] == b[j] then
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memo[i + 1, j + 1] = memo[i, j]
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else
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memo[i + 1, j + 1] = [
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memo[i + 1, j],
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memo[i, j + 1],
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memo[i, j]
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].min + 1
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end
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end
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end
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return memo[a.size, b.size]
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end
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