#include <iostream>
#include <string>
using namespace std;

//BF算法实现
int BF(string _str, string _patnStr)
{
	int i = 0, j = 0;

	while ((_str[i] != '\0') && (_patnStr[j] != '\0'))
	{
		if (_str[i] == _patnStr[j])
		{
			++i;
			++j;
		}
		else
		{
			i = i - j + 1;
			j = 0;
		}
	}

	if (_patnStr[j] == '\0')
		return i - j + 1;
	return -1;
}

//KMP算法实现
int KMP(string _str, string _patnStr)
{
	int i = 0, j = -1;
	int *next = new int[_patnStr.length()];
	next[0] = -1;

	while (i < _patnStr.length())
	{
		if (j == -1 || _patnStr[i] == _patnStr[j])
		{
			++i;
			++j;
			next[i] = j;
		}
		else
			j = next[j];
	}

	i = 0;
	j = 0;

	while (i < _str.length() && j < _patnStr.length())
	{
		if (j == -1 || _str[i] == _patnStr[j])
		{
			i++;
			j++;
		}
		else
			j = next[j];
	}

	if (j == _patnStr.length())
		return i - j + 1;
	else
		return -1;
}

int main()
{
	string str = "aaaaacaaaaa";
	string patnStr = "ac";

	cout << BF(str, patnStr) << endl;
	cout << KMP(str, patnStr) << endl;
	
	return 0;
}

输出

5
5