giles
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Recursive Levenshtein edit distance with no memoization (the test
strings are short enough for the exponential-without-memo version to
fit in <2 minutes on contended hosts). Sums distances for five short
pairs:
('abc','abx') + ('ab','ba') + ('abc','axyc') + ('','abcd') + ('ab','')
= 1 + 2 + 2 + 4 + 2 = 11
Exercises:
* curried four-arg recursion
* s.[i] equality test (char comparison)
* min nested twice for the three-way recurrence
* mixed empty-string base cases
19 lines
400 B
OCaml
19 lines
400 B
OCaml
let rec lev s1 s2 i j =
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if i = 0 then j
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else if j = 0 then i
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else if s1.[i - 1] = s2.[j - 1] then
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lev s1 s2 (i - 1) (j - 1)
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else
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1 + min (lev s1 s2 (i - 1) j)
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(min (lev s1 s2 i (j - 1)) (lev s1 s2 (i - 1) (j - 1)))
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let dist s1 s2 = lev s1 s2 (String.length s1) (String.length s2)
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;;
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dist "abc" "abx"
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+ dist "ab" "ba"
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+ dist "abc" "axyc"
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+ dist "" "abcd"
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+ dist "ab" ""
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