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Knuth-Morris-Pratt linear-time string search: - kmp_table builds failure function in O(|pattern|) - kmp_search scans text once in O(|text|), counting matches - After a hit, k := t.(n-1) so overlapping matches still count kmp_search "abababcabababcababcc" "abab" = 5 Hits at positions 0, 2, 7, 9, 14 (overlapping at 0/2 and 7/9). Tests: nested while-inside-for, char inequality (.<>), pat.[i] string indexing, Array.make 0, combined string + array indexing. 140 baseline programs total.
38 lines
782 B
OCaml
38 lines
782 B
OCaml
let kmp_table pat =
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let n = String.length pat in
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let t = Array.make n 0 in
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let k = ref 0 in
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for i = 1 to n - 1 do
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while !k > 0 && pat.[!k] <> pat.[i] do
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k := t.(!k - 1)
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done;
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if pat.[!k] = pat.[i] then k := !k + 1;
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t.(i) <- !k
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done;
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t
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let kmp_search text pat =
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let m = String.length text in
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let n = String.length pat in
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if n = 0 then 0
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else begin
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let t = kmp_table pat in
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let count = ref 0 in
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let k = ref 0 in
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for i = 0 to m - 1 do
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while !k > 0 && pat.[!k] <> text.[i] do
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k := t.(!k - 1)
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done;
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if pat.[!k] = text.[i] then k := !k + 1;
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if !k = n then begin
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count := !count + 1;
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k := t.(n - 1)
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end
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done;
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!count
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end
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;;
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kmp_search "abababcabababcababcc" "abab"
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