Implement strStr().
Returns the index of the first occurrence of needle in haystack, or -1 if needle is not part of haystack.
Seen this question in a real interview before?
题意：返回一个字符串，在另一个字符串中的位置，如果没有的话，就返回-1。
c++:
class Solution {
public:
int strStr(std::string haystack, std::string needle) {
int len = needle.size();
if (haystack.size() < len) return -1;
for (int idx=0; idx <= haystack.size()- len; idx++){
if (std::string (haystack.begin()+idx, haystack.begin()+idx+len) == needle) return idx;
}
return -1;
}
};
