71. Simplify Path

class Solution {
public:
    string simplifyPath(string path)
    {
        vector<string> dir;
        stringstream ss(path);
        string token;
        while(getline(ss, token, '/'))
        {
            if(token == "..")
            {
                if (!dir.empty()) dir.pop_back();
            }
            else if (!token.empty() && token != ".")
            {
                dir.push_back(token);
            }
        }
        string res;
        for (auto s : dir) res += "/" + s;
        return res.empty() ? "/" : res;
    }
};

• T: $O(n)$
• S: $O(n)$