KMP算法

class KMP
{
public:
	void getNext(int* next, const string str)
	{
		int j = -1;
		next[0] = j;
		for (int i = 1; i < str.size(); i++)// 注意i从1开始
		{
			while (j >= 0 && str[i] != str[j+1])// 前后缀不相同了
			{
				j = next[j];// 向前回溯
			}
			if (str[i] == str[j+1]) // 找到相同的前后缀
			{
				j++;
			}
			next[i] = j;// 将j（前缀的长度）赋给next[i]
		}
	}

	int sameStr(string str1, string str2)
	{
		if (str2.size() == 0)
			return 0;
		
		int* next = new int[str2.size()];
		int j = -1;//因为next数组里记录的起始位置为 - 1
		getNext(next, str2);
		for (int i = 0; i < str1.size(); i++)
		{
			while (j >= 0 && str1[i] != str2[j+1])
			{
				j = next[j];
			}
			if (str1[i] == str2[j+1])
			{
				j++;
			}
			if (j == str2.size() - 1)
			{
				return i - str2.size() + 1;
			}
		}
		return -1;
	}
};