C++ Program to Implement KMP Pattern Searching Algorithm

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.

```
/*
```

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

```
 */
```
```
#include <iostream>
```
```
#include <cstring>
```
```
using namespace std;
```
```
void preKMP(string pattern, int f[])
```
```
{
```
```
    int m = pattern.length(), k;
```
```
    f[0] = -1;
```
```
    for (int i = 1; i < m; i++)
```
```
    {
```
```
        k = f[i - 1];
```
```
        while (k >= 0)
```
```
        {
```

            if (pattern[k] == pattern[i - 1])

```
                break;
```
```
            else
```
```
                k = f[k];
```
```
        }
```
```
        f[i] = k + 1;
```
```
    }
```
```
}
```
```
 
```

//check whether target string contains pattern

```
bool KMP(string pattern, string target)
```
```
{
```
```
    int m = pattern.length();
```
```
    int n = target.length();
```
```
    int f[m];     
```
```
    preKMP(pattern, f);     
```
```
    int i = 0;
```
```
    int k = 0;        
```
```
    while (i < n)
```
```
    {
```
```
        if (k == -1)
```
```
        {
```
```
            i++;
```
```
            k = 0;
```
```
        }
```

        else if (target[i] == pattern[k])

```
        {
```
```
            i++;
```
```
            k++;
```
```
            if (k == m)
```
```
                return 1;
```
```
        }
```
```
        else
```
```
            k = f[k];
```
```
    }
```
```
    return 0;
```
```
}
```
```
 
```
```
int main()
```
```
{
```

    string tar = "san and linux training";

```
    string pat = "lin";
```
```
    if (KMP(pat, tar))
```

        cout<<"'"<<pat<<"' found in string '"<<tar<<"'"<<endl;

```
    else
```

        cout<<"'"<<pat<<"' not found in string '"<<tar<<"'"<<endl;

```
    pat = "sanfoundry";
```
```
    if (KMP(pat, tar))
```

        cout<<"'"<<pat<<"' found in string '"<<tar<<"'"<<endl;

```
    else
```

        cout<<"'"<<pat<<"' not found in string '"<<tar<<"'"<<endl;

```
    return 0;
```
```
}
```

$ 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

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