leetcode 28（简单kmp）

void GetNext(string &needle,int next[])
    {
        next[0]=-1;
        int k=-1;
        int len=needle.size();
        for(int i=1;i<len;i++)
        {
            while(k!=-1&&needle[k+1]!=needle[i])
                k=next[k];
            if(needle[k+1]==needle[i])
            {
                k++;
            }
            next[i]=k;
        }
    }
    
    int strStr(string haystack, string needle) {
        int nlen=needle.size();
        int hlen=haystack.size();
        if(nlen==0)
            return 0;
        if(hlen==0)
            return -1;
        int *next=new int[nlen];
        GetNext(needle,next);
        int k=-1;
        for(int i=0;i<hlen;i++)
        {
            while(k!=-1&&needle[k+1]!=haystack[i])
                k=next[k];
            if(needle[k+1]==haystack[i])
            {
                k++;
                if(k==nlen-1)
                    return i-k;
            }
        }
        return -1;
    }