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class Solution {
public:
    int strStr(const char *source, const char *target) {
        // check if source or target is nullptr
        if (source == nullptr || target == nullptr) {
            return -1;
        }
        string s(source), t(target);
        if (t.size() == 0) {
            return 0;
        }

        for (int i = 0; i < s.size() - t.size() + 1; i++) {
            if (s[i] != t[0]) {
                continue;
            }
            for (int j = 1; j < t.size(); j++) {
                if (s[i + j] != t[j]) {
                    break;
                }
                if (j == t.size() - 1) {
                    return i;
                }
            }
        }

        return -1;
    }
};