Knuth-Morris-Pratt string search

Emacs Lisp

<lang lisp> (defun kmp_compile_pattern (pattern)

 "Compile pattern to DFA."

 (defun create-2d-array (x y init)
   (let ((arr1 (make-vector x nil)))
     (dotimes (i x)

(aset arr1 i (make-vector y init)) )

     arr1 ) )
 
 (let* ((patLen (length pattern))

(R 256)

        (restartPos 0)

(dfa (create-2d-array R patLen 0)))

   (aset (aref dfa (elt pattern 0)) 0 1)

   (let ((patPos 0))
     (while (progn (setq patPos (1+ patPos)) (< patPos patLen))

(dotimes (c R) (aset (aref dfa c) patPos (aref (aref dfa c) restartPos)) )

(aset (aref dfa (elt pattern patPos)) patPos (1+ patPos)) (setq restartPos (aref (aref dfa (elt pattern patPos)) restartPos) ) )

     )
   dfa )
 )

(defun kmp_search (pattern text)

 (let ((dfa (kmp_compile_pattern pattern)))

   (let ((textPos 0) (patPos 0) (N (length text)) (M (length pattern)))
     (while (and (< textPos N) (< patPos M))

(setq patPos (aref (aref dfa (elt text textPos)) patPos)) (setq textPos (1+ textPos)) )

     (if (= patPos M) (- textPos M) N ) ) ) )

</lang>