KMP算法

void getNext(string needle, int *next)
{
    int l = needle.length(), i, k;
    next[0] = -1;
    k = -1;
    for(i = 0; i < l-1;)
    {
        if(-1 == k || needle[i] == needle[k])
            next[++i] = ++k;
        else
            k = next[k];
    }
}

int KMP(string s1, string s2, int *next)
{
    int l1 = s1.length(), l2 = s2.length(), i, j;
    for(i = 0, j = 0; i < l1;)
    {
        if(-1 == j || s1[i] == s2[j])
        {
            i++;
            j++;
        }
        else
            j = next[j];
        if(j == l2)
            return i-j; //返回子串第一次出现的位置下标
    }
    return -1;
}