Method getNext

28. Implement strStr()/Solution.cpp:53–67

public:

    vector<int> getNext(string pat) {
        vector<int> next (pat.size());
        next[0] = -1;
        int i = 0, j = -1;
        while ( i < pat.size() - 1 ) {
            if (j == -1 or pat[i] == pat[j]) {
                i ++ ;
                j ++ ;
                next[i] = j;    
            } else {
                j = next[j];
            }
        }
        return next;
    }

    int strStr(string haystack, string needle) {
        if (needle.empty()) return 0;