0028.cpp

class Solution {
public:
    int strStr(string haystack, string needle) {
        const int m = haystack.size();
        const int n = needle.size();

        for (int i = 0; i < m - n + 1; i++)
            if (haystack.substr(i, n) == needle)
                return i;

        return -1;
    }
};