C++ Program to Implement Knuth–Morris–Pratt Algorithm (KMP)

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This C++ Program demonstrates the implementation of Knuth–Morris–Pratt Algorithm popularly known as KMP.

Here is source code of the C++ Program to implement Knuth–Morris–Pratt Algorithm (KMP). The C++ program is successfully compiled and run on a Linux system. The program output is also shown below.

  1. /*
  2.  * C++ Program to Implement Knuth–Morris–Pratt Algorithm (KMP)
  3.  */
  4. #include <iostream>
  5. #include <cstring>
  6. using namespace std;
  7. void preKMP(string pattern, int f[])
  8. {
  9.     int m = pattern.length(), k;
  10.     f[0] = -1;
  11.     for (int i = 1; i < m; i++)
  12.     {
  13.         k = f[i - 1];
  14.         while (k >= 0)
  15.         {
  16.             if (pattern[k] == pattern[i - 1])
  17.                 break;
  18.             else
  19.                 k = f[k];
  20.         }
  21.         f[i] = k + 1;
  22.     }
  23. }
  24.  
  25. //check whether target string contains pattern 
  26. bool KMP(string pattern, string target)
  27. {
  28.     int m = pattern.length();
  29.     int n = target.length();
  30.     int f[m];     
  31.     preKMP(pattern, f);     
  32.     int i = 0;
  33.     int k = 0;        
  34.     while (i < n)
  35.     {
  36.         if (k == -1)
  37.         {
  38.             i++;
  39.             k = 0;
  40.         }
  41.         else if (target[i] == pattern[k])
  42.         {
  43.             i++;
  44.             k++;
  45.             if (k == m)
  46.                 return 1;
  47.         }
  48.         else
  49.             k = f[k];
  50.     }
  51.     return 0;
  52. }
  53.  
  54. int main()
  55. {
  56.     string tar = "san and linux training";
  57.     string pat = "lin";
  58.     if (KMP(pat, tar))
  59.         cout<<"'"<<pat<<"' found in string '"<<tar<<"'"<<endl;
  60.     else
  61.         cout<<"'"<<pat<<"' not found in string '"<<tar<<"'"<<endl;
  62.     pat = "sanfoundry";
  63.     if (KMP(pat, tar))
  64.         cout<<"'"<<pat<<"' found in string '"<<tar<<"'"<<endl;
  65.     else
  66.         cout<<"'"<<pat<<"' not found in string '"<<tar<<"'"<<endl;
  67.     return 0;
  68. }

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$ g++ kmp.cpp
$ a.out
 
'lin' found in string 'san and linux training'
'sanfoundry' not found in string 'san and linux training'
 
------------------
(program exited with code: 1)
Press return to continue

Sanfoundry Global Education & Learning Series – 1000 C++ Programs.

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Manish Bhojasia, a technology veteran with 20+ years @ Cisco & Wipro, is Founder and CTO at Sanfoundry. He is Linux Kernel Developer & SAN Architect and is passionate about competency developments in these areas. He lives in Bangalore and delivers focused training sessions to IT professionals in Linux Kernel, Linux Debugging, Linux Device Drivers, Linux Networking, Linux Storage, Advanced C Programming, SAN Storage Technologies, SCSI Internals & Storage Protocols such as iSCSI & Fiber Channel. Stay connected with him @ LinkedIn