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(***********************************************************************)
(* *)
(* Objective Caml *)
(* *)
(* Pierre Weis, projet Cristal, INRIA Rocquencourt *)
(* *)
(* Copyright 2001 Institut National de Recherche en Informatique et *)
(* en Automatique. All rights reserved. This file is distributed *)
(* only by permission. *)
(* *)
(***********************************************************************)
(* Find the first occurrence of string [p] (the so-called ``pattern'')
into the string [s].
Elaborated algorithm.
Knuth-Morris-Pratt algorithm following Sedgewick's book "Algorithms".
The Caml code was proved correct in the Coq Proof Assistant.
Based on a mail to the Caml list by Jean-Christophe FILLIATRE. *)
let init_next p =
let m = String.length p in
let next = Array.create m 0 in
let i = ref 1 and j = ref 0 in
while !i < m - 1 do
if p.[!i] = p.[!j] then begin incr i; incr j; next.(!i) <- !j end else
if !j = 0 then begin incr i; next.(!i) <- 0 end else j := next.(!j)
done;
next;;
let kmp p =
let next = init_next p
and m = String.length p in
function s ->
let n = String.length s
and i = ref 0
and j = ref 0 in
while !j < m && !i < n do
if s.[!i] = p.[!j] then begin incr i; incr j end else
if !j = 0 then incr i else j := next.(!j)
done;
if !j >= m then !i - m else raise Not_found;;
let find_pat p s =
try
let i = kmp p s in
print_string "Match found at character ";
print_int i;
print_newline ();
exit 0
with Not_found ->
print_string "Pattern ";
print_string p;
print_string " does not match string ";
print_string s;
print_newline ();
exit 2;;
let usage () =
print_string
"Usage: kmp <pat> <str>\n\
returns the index of the first occurrence of <pat> in string <str>\n";
exit 2;;
let main () =
let args = Sys.argv in
if Array.length args < 2 then usage () else
let p = Sys.argv.(1)
and s = Sys.argv.(2) in
find_pat p s;;
if !Sys.interactive then () else main ();;
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