Python implementations of string matching

The core problem with all string matching algorithms is how to move the pattern string backwards when a mismatch occurs

First, the violent matching algorithm

If you want to match a string s and a pattern string p, then start with i=0 to match s[i: (I+len (P))], simple and rude, the code is as follows:

def matcher (T, p):     # param t:the String to check    # param P:pattern    n = len (t)    = len (p)    for in xrange (0, n-m+1):          if return True

Second, KMP algorithm

See also: http://blog.csdn.net/v_july_v/article/details/7041827

In simple terms, when matching the string s and pattern string p, when s[i] and P[j] do not match, do not backtrack s, but will shift p to a certain number of digits to start matching. The right shift number is determined by the following rules: if P[J] precedes the same string length as the maximum length of the string L, then move right (matched string length-L), text description is more abstract, see the above blog content

defPMT (s):"""partialmatchtable"""prefix= [S[:i+1] forIinchRange (len (s)-1)] Postfix= [S[i+1]: forIinchRange (len (s)-1)] Intersection= List (set (prefix) & Set (Postfix))#get the same prefix    ifintersection:returnLen (Intersection[0])#get the longest prefix    returnodefKMP (T, p):#t:the string to check    #P:patterni =0 whileI < Len (t)-Len (p) + 1: Match=True forJinchRange (len (P)):ifT[I+J]! =P[j]: Match=False Break            ifmatch:returnTrue#KMP            ifj:i+ = J-PMT (P[:j])Else: i + = 1returnFalse

The above code reference http://cnblogs.com/goodspeed/p/3295456.html

In addition, there are BM algorithm, Sunday algorithm and Horspool algorithm, the latter two are the variants in the migration, "BM algorithm in practical applications than KMP algorithm three to five times times faster."

Python implementations of string matching