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local function min(a, b, c)
local min_val = a
if b < min_val then min_val = b end
if c < min_val then min_val = c end
return min_val
end
----------------------------------
--- Levenshtein distance function.
-- @tparam string s1
-- @tparam string s2
-- @treturn number the levenshtein distance
-- @within Metrics
return function(s1, s2)
if s1 == s2 then return 0 end
if s1:len() == 0 then return s2:len() end
if s2:len() == 0 then return s1:len() end
if s1:len() < s2:len() then s1, s2 = s2, s1 end
local t = {}
for i=1, #s1+1 do
t[i] = {i-1}
end
for i=1, #s2+1 do
t[1][i] = i-1
end
local cost
for i=2, #s1+1 do
for j=2, #s2+1 do
cost = (s1:sub(i-1,i-1) == s2:sub(j-1,j-1) and 0) or 1
t[i][j] = min(
t[i-1][j] + 1,
t[i][j-1] + 1,
t[i-1][j-1] + cost)
end
end
return t[#s1+1][#s2+1]
end
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