c++ custom sort for unordered_map

The sort in c++ can only sort the vector, so if you customize the unordered_map sort, you need to put it in the vector.
Take lc386 as an example:

class Solution {
    
    
public:
    static bool cmp(pair<string, int> &a, pair<string, int> &b){
    
    
        return a.first < b.first;
    }

    vector<int> lexicalOrder(int n) {
    
    
        vector<int> result;
        vector<pair<string, int>> tVector;
        unordered_map<string, int> mapp;
        for(int i = 0;i<n;i++){
    
    
            mapp[to_string(i+1)] = i+1;
        }
        for(auto iter = mapp.begin();iter!=mapp.end();iter++){
    
    
            tVector.push_back(make_pair(iter->first, iter->second));
        }
        sort(tVector.begin(), tVector.end(), cmp);
        for(auto it = tVector.begin();it!=tVector.end();it++){
    
    
            result.push_back(it->second);
        }
    return result;
    }
};