1233. Remove Sub-Folders from the Filesystem

class Solution {
public:
    vector<string> removeSubfolders(vector<string>& folder) {
        sort(folder.begin(), folder.end());
        vector<string> res;
        res.push_back(folder[0]);
        for(int i=1;i<folder.size();++i) {
            string s = res.back()+"/";
            if (folder[i].substr(0, s.size())!=s) {
                res.push_back(folder[i]);
            }
        }
        return res;
    }
};