Algorithm-Rabin-Karp Algorithm for String Matching

Algorithm-Rabin-Karp Algorithm for String Matching
Preface

The Rabin-Karp string matching algorithm is similar to the simple string matching algorithm described earlier. It also compares each character. The difference is that Rabin-Karp uses character preprocessing, that is to say, the corresponding hexadecimal number and modulo operation are performed for each character. It is similar to calculating its function value through a function and comparing the function value of each character. The pre-processing time is O (m), and the matching time is O (n-m + 1) m ).

Implementation of Rabin-Karp Algorithm

Pseudocode:

 

Rabin_Karp_search (T, P, d, q) n = T. length; m = P. length; h = d ^ (m-1) mod q; p = 0; t = 0; for I = 1 to m p = (d * p + P [I]) mod q; t = (d * t + T [I]) mod q; for I = 0 to n-m if p = t if P [1 .. m] = T [I + 1 .. I + m] printPattern occurs with shifti if I
 
  
 
  
Source code:
  
 
  
// Rabin Karp Algorithm  #include
   
    #include
    
     using namespace std; void Rabin_Karp_search(const string &T, const string &P, int d, int q){    int m = P.length();    int n = T.length();    int i, j;    int p = 0;  // hash value for pattern    int t = 0; // hash value for txt    int h = 1;      // The value of h would be pow(d, M-1)%q    for (i = 0; i < m-1; i++)        h = (h*d)%q;      // Calculate the hash value of pattern and first window of text    for (i = 0; i < m; i++)    {        p = (d*p + P[i])%q;        t = (d*t + T[i])%q;    }      // Slide the pattern over text one by one     for (i = 0; i <= n - m; i++)    {                // Chaeck the hash values of current window of text and pattern        // If the hash values match then only check for characters on by one        if ( p == t )        {            /* Check for characters one by one */            for (j = 0; j < m; j++)               if (T[i+j] != P[j])   break;                        if (j == m)  // if p == t and pat[0...M-1] = txt[i, i+1, ...i+M-1]               cout<