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?

題意：返回一個字符串，在另一個字符串中的位置，如果沒有的話，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;
    }
};