LeetCode_implement strstr ()

 Implement strStr().

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

　　KMP :

class Solution {
public:
    void calculatNext(char *pattern)
    {

       int i = , k = -;
       next[] = -;
       while( i < sizeNeed -) //计算next[i+1]
       {

         while(k >=  && pattern[i] != pattern[k]) k = next[k];

         i++; k++;

         next[i] = pattern[i] == pattern[k] ? next[k] : k;

       }
    }
    char *strStr(char *haystack, char *needle) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        sizeHay = strlen(haystack);
        sizeNeed = strlen(needle);

        if(sizeNeed == )  return haystack;
        next.resize(sizeNeed);

        calculatNext(needle);

        int i =  , j = ;

        while(i< sizeHay && j < sizeNeed)
        {
            if(j == - || haystack[i] == needle[j]){
              i++;j++;
            }else
              j = next[j];
        }

        if(j >= sizeNeed)
          return haystack+(i - j);
         else
          return NULL ;
    }

private :
  int sizeHay;
  int sizeNeed ;
  vector<int> next ;
};