Implement strStr()

Implement strStr().

Returns the index of the first occurrence of needle in haystack, or -1 if needle is not part of haystack.

Update (2014-11-02):
The signature of the function had been updated to return the index instead of the pointer. If you still see your function signature returns achar * or String, please click the reload button to reset your code definition.

Solution:

class Solution {public:    void getNext(string needle, vector<int> &next)    {        int i = 0, j = -1;        next[i] = j;        while(i < needle.length())        {            while(j != -1 && needle[i] != needle[j]) j = next[j];            next[++i] = ++j;        }    }    int strStr(string haystack, string needle) {        vector<int> next(needle.length()+1);        getNext(needle, next);        int i = 0, j = 0;        int hlen = haystack.length();        int nlen = needle.length();        while(i < hlen && j < nlen)        {            if(j == -1 || haystack[i] == needle[j])            {                ++i;                ++j;            }            else            {                j = next[j];            }        }        if(j == nlen) return i - j;        else return -1;    }};