KMP算法

//KMP算法的C++实现
#include <iostream>
#include <string>

using namespace std;

/******************求子串的匹配数组**********************/
int *pre(string &sub)
{
	int m = sub.length();
	int *k = new int[m];
	k[0] = -1;
	int q = -1;
	for(int i=1; i<m; i++)
	{
		while( q>-1 && sub.at(i)!=sub.at(q+1) )
			q = k[q];
		if(sub.at(i)==sub.at(q+1))
			q++;
		k[i] = q;
	}
	return k;
}

/************************求匹配串***********************/
int kmp(string &s, string &sub)
{
	int m = s.length();
	int n = sub.length();
	int *k = pre(sub);
	int q = -1;
	for(int i = 0 ; i<m ; i++)
	{
		while(q > -1 && s.at(i) != sub.at(q+1))
		{
			q = k[q];
		}
		if(sub.at(q+1) == s.at(i))
			q++;
		if(q == n-1)
		{
			cout << "Pattern occurs with shift " << i-n+1 << endl;
			q = k[q];
		}
	}
	return 0;
}




int main()
{
	string s = "dfdfdferdfdfdferdfdfdfdfgfgdfdfdfdfdfdfdfdfdferdfdfddfdffffdfdfdfdfdfdfdfdferewrdewreddfdfdf";//需要比较的串
	string sub = "dfdfdfer";//有待比较的串
	kmp(s,sub);
	return 0;
}