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

KMP算法请移步[这篇博客](https://github.com/ZXZxin/ZXBlog/blob/master/%E6%95%B0%E6%8D%AE%E7%BB%93%E6%9E%84%E7%AE%97%E6%B3%95/String/KMP/Hdu%20-%201711 ...