Replace every element with least greater elements on its right

class Solution{
    public:
    vector<int> findLeastGreater(vector<int>& arr, int n) {
       set<int> s;

        vector<int> v;

        for(int i=n-1;i>=0;i--){

            int key = arr[i];

            auto it=s.upper_bound(key);

            if(it==s.end()){

                v.push_back(-1);

            }

            else{

                v.push_back(*it);

            }

            s.insert(arr[i]);

        }

        reverse(v.begin(),v.end());

        return v;
    }
};