KMP

#include <iostream>
#include <string>
#include <vector>
using namespace std;
void COMPUTE_PREIFX_FUNCTION(string P,vector<int>& pi);
void KMP_MATCHER(string &T,string &P);
 
void main()
{
	string T="BBC ABCDAB ABCDABCDABDEFABCDABDff";
	string P="ABCDABD";
	
	KMP_MATCHER(T,P);
}
void COMPUTE_PREIFX_FUNCTION(string P,vector<int>& pi)
{
	int m=P.size();
	pi[0]=0;
	pi[1]=0;
	int k=0;
	for (int q=2;q<m;q++)
	{
		while (k>0&&P[k+1]!=P[q])
		{
			k=pi[k];
		}
		if (P[k+1]==P[q])
		{
			k=k+1;
		}
		pi[q]=k;
	}
}
void KMP_MATCHER(string &T,string &P)
{
	T="%"+T;
	P="*"+P;
	int m=P.size();
	vector<int> pi(m);
	int n=T.size();
	COMPUTE_PREIFX_FUNCTION(P,pi);
	int q=0;
	int i;
	for (i=1;i<n;i++)
	{
		while (q>0&&P[q+1]!=T[i])
		{
			q=pi[q];
		}
		if (P[q+1]==T[i])
		{
			q=q+1;
		}
		if (q==m-1)
		{
			cout<<"pattern occurs with shift  "<<i-q<<endl;
			q=pi[q];
		}
	}
}