programming-examples/c++/11_Sets_&_Strings/C++ Program to Implement Knuth–Morris–Pratt Algorithm (KMP).cpp

/*
 * 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;
}

/*
'lin' found in string 'san and linux training'
'sanfoundry' not found in string 'san and linux training'