giles
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Iterative Levenshtein DP with rolling 1D arrays for O(min(m,n)) space. Distances: kitten -> sitting : 3 saturday -> sunday : 3 abc -> abc : 0 "" -> abcde : 5 intention -> execution : 5 ---------------------------- total : 16 Complementary to the existing levenshtein.ml which uses the exponential recursive form (only sums tiny strings); this one is the practical iterative variant used for real ED. Tests the recently-fixed <- with bare `if` rhs: curr.(j) <- (if m1 < c then m1 else c) + 1 153 baseline programs total.
31 lines
761 B
OCaml
31 lines
761 B
OCaml
let lev_iter s1 s2 =
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let m = String.length s1 in
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let n = String.length s2 in
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let prev = Array.make (n + 1) 0 in
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let curr = Array.make (n + 1) 0 in
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for j = 0 to n do prev.(j) <- j done;
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for i = 1 to m do
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curr.(0) <- i;
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for j = 1 to n do
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if s1.[i - 1] = s2.[j - 1] then
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curr.(j) <- prev.(j - 1)
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else begin
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let a = prev.(j) in
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let b = curr.(j - 1) in
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let c = prev.(j - 1) in
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let m1 = if a < b then a else b in
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curr.(j) <- (if m1 < c then m1 else c) + 1
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end
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done;
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for j = 0 to n do prev.(j) <- curr.(j) done
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done;
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prev.(n)
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;;
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lev_iter "kitten" "sitting"
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+ lev_iter "saturday" "sunday"
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+ lev_iter "abc" "abc"
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+ lev_iter "" "abcde"
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+ lev_iter "intention" "execution"
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