---- KMP string matching algorithm Algorithms

Previous Violence Act mentioned in string matching algorithm, but obviously there is a problem Violence Act: time to move only one character. But in fact, for different match situations, each movement interval can be larger, but each time there is no need to move a:

About KMP algorithm description, we recommend a blog: https://blog.csdn.net/weixin_36604953/article/details/78576637

The blog describes in detail the principles of KMP algorithm. The following code implements the KMP algorithm:

1  // using a brute force method, KMP completed character string matching algorithm Algorithm 
2 # the include " the iostream " 
. 3 #include " String " 
. 4 #include " Vector " 
. 5  the using  namespace STD;
 . 6 Vector < int > & BFmatch ( String &, String &, Vector < int > & );
 . 7 Vector < int > & KMPStrMatch ( String &, String &, Vector < int > & );
 8 voidShowpos (Vector < int > & );
 . 9  int main ()
 10  {
 . 11      String ModelStr, SonStr;
 12 is      Vector < int > POS;
 13 is      COUT << " Please enter a string to be matched: " ;
 14      CIN >> ModelStr;
 15      << COUT endl;
 16      COUT << " Please enter substring: " ;
 . 17      CIN >> SonStr;
 18 is      COUT << endl;
 . 19      // BFmatch (ModelStr, SonStr, POS);
20     KMPStrMatch(ModelStr, SonStr, pos);
21     ShowPos(pos);
22     system("pause");
23 }
24 vector<int>& BFmatch(string & ModelStr, string & SonStr,vector<int>& pos)
25 {
26     for (int i = 0; i < ModelStr.size(); i++)
27     {
28         int k = 0;
29         for (int j = i; k < SonStr.size(); j++, k++)
30         {
31             if (SonStr[k] == ModelStr[j])
32                 continue;
33             else
34                 break;
35         }
36         if (k == SonStr.size())
37             pos.push_back(i);
38     }
39     return pos;
40 }
41 void ShowPos(vector<int>& pos)
42 {
43     if (pos.size() != 0)
44     {
45         cout << "the first position of MatchingStr:";
46         for (int i = 0; i < pos.size(); i++)
47         {
48             cout << pos[i] << "\t";
49         }
50         cout << endl;
51     }
52     else
53         cout << "no such string!" << endl;
54 }
55 vector<int>& KMPStrMatch(string & ModelStr, string & SonStr, vector<int>& pos)
56 {
57     string ComStr;
58     string tmp1, tmp2;
59     int j = 0, i = 0, len = 0;;
60     while(j< (ModelStr.size()- SonStr.size()+1))
61     {
62         if (ModelStr[j] != SonStr[0])
63         {
64             j++;
65             continue;//首位不匹配直接加1
66          }
 67          the else 
68          {
 69              the while ((J <ModelStr.size ()) && (ModelStr [J] == SonStr [I])) // && foregoing constraint ensures that memory does not occur bounds
 70              {
 71 is                  J ++ ;
 72                  I ++ ;
 73 is              }
 74              IF (I == SonStr.size ())
 75                  pos.push_back (J - SonStr.size ());
 76              J = J - I;
 77              ComStr SonStr.substr = ( 0 , I - . 1 );
 78              for (int q = 1; q < ComStr.size(); q++)
79             {
80                 tmp1=ComStr.substr(q, ComStr.size() - 1);
81                 tmp2=ComStr.substr(0, ComStr.size() - 1 - q);
82                 if (tmp1 == tmp2)
83                     len++;
84             }
85             j = j + i-len;
86             i = 0;
87             len = 0;
88         }
89      }
 90      return postage;
91 }

In short, KMP's core idea is: to decide to move the length of the string to be matched by the length of the matching portion of the string, rather than just moving each one.

---- KMP string matching algorithm Algorithms

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