Implement strStr()

Implement strStr().

Returns a pointer to the first occurrence of needle in haystack, or null if needle is not part of haystack.

class Solution {
public:
    char *strStr(char *haystack, char *needle) 
    {
        //BF
        /*
        for(char* pstart=haystack;(*pstart)!=NULL;pstart++)
        {
            char* p2=needle;
            for(char* p1=pstart;(*p1)!=NULL && (*p2)!=NULL;p1++,p2++)
            {
                if((*p1)!=(*p2)) break;
            }
            if((*p2)==NULL) return pstart;
        }
        return NULL;
        */
        
        //KMP
        int len=strlen(needle);
        if(len==0) return haystack;
        int* find=new int[len];
        find[0]=0;
        for(int i=1,j=0;i<len;i++)
        {
            while(j>0 && needle[i]!=needle[j]) j=find[j-1];
            if(needle[i]==needle[j]) j++;
            find[i]=j;
        }
        int textlen=strlen(haystack);
        for(int i=0,j=0;i<textlen;i++)
        {
            while(j>0 && haystack[i]!=needle[j]) j=find[j-1];
            if(haystack[i]==needle[j]) j++;
            if(j==len) return haystack+i-len+1;
        }
        return NULL;
    }
};