43 lines
1004 B
Python
43 lines
1004 B
Python
|
#! /usr/bin/env python
|
||
|
|
|
||
|
|
# Description: Knuth-Morris-Pratt algorithm
|
||
|
|
|
||
|
|
"""Knuth-Morris-Pratt algorithm
|
||
|
|
|
||
|
|
This is a direct transaltion of the KMP algorithm in the book
|
||
|
|
"Introduction to Algorithms" by Cormen, Lieserson, and Rivest. See that
|
||
|
|
book for an explanation of why this algorithm works. It's pretty cool.
|
||
|
|
|
||
|
|
The only things I changed were some offsets, to cope with the fact that
|
||
|
|
Python arrays are 0-offset.
|
||
|
|
|
||
|
|
"""
|
||
|
|
|
||
|
|
__author__ = 'Neale Pickett <neale@woozle.org>'
|
||
|
|
|
||
|
|
def compute_prefix_function(p):
|
||
|
|
m = len(p)
|
||
|
|
pi = [0] * m
|
||
|
|
k = 0
|
||
|
|
for q in range(1, m):
|
||
|
|
while k > 0 and p[k] != p[q]:
|
||
|
|
k = pi[k - 1]
|
||
|
|
if p[k] == p[q]:
|
||
|
|
k = k + 1
|
||
|
|
pi[q] = k
|
||
|
|
return pi
|
||
|
|
|
||
|
|
def kmp_matcher(t, p):
|
||
|
|
n = len(t)
|
||
|
|
m = len(p)
|
||
|
|
pi = compute_prefix_function(p)
|
||
|
|
q = 0
|
||
|
|
for i in range(n):
|
||
|
|
while q > 0 and p[q] != t[i]:
|
||
|
|
q = pi[q - 1]
|
||
|
|
if p[q] == t[i]:
|
||
|
|
q = q + 1
|
||
|
|
if q == m:
|
||
|
|
return i - m + 1
|
||
|
|
return -1
|