Implement strStr()&BF&KMP

class Solution {
public:
    char *strStr(char *haystack, char *needle) {
        if(!*needle)
            return haystack;
            
        char *p,*q;
        char *p_advance=haystack;
        
        for(q=&needle[1];*q;++q)
            ++p_advance;
            
        for(p=haystack;*p_advance;++p_advance)
        {
            char *p_old=p;
            q=needle;
            while(*p&&*q&&*p==*q)
            {
                ++p;
                ++q;
            }
            if(!*q)
                return p_old;
            p=p_old+1;
        }
        return NULL;
    }
};

class Solution {
public:
    char *strStr(char *haystack, char *needle) {
        if(!*needle)
            return haystack;
            
        int *next=new int[strlen(needle)];
        getNext(needle,next);
        
        for(int i=0,j=0;i<strlen(haystack);)
        {
            if(j==-1||haystack[i]==needle[j])
            {
                ++i;
                ++j;
            }
            else
                j=next[j];
            
            if(j==strlen(needle))
                return (char*)(i-strlen(needle)+haystack);
        }
        return NULL;
    }
    
    //array of next
    //as for char *s="ababa",the corresponding array is:-1,0,0,1,2
    void getNext(char *needle,int next[])
    {
        next[0]=-1;
        int k=-1;
        int j=0;
        while(j<strlen(needle)-1)
        {
            if(k==-1||needle[j]==needle[k])
            {
                ++j;
                ++k;
                next[j]=k;
            }
            else
                k=next[k];
        }
    }
};