vector<int> icecreamParlor(int m, vector<int> arr){
    vector <int> result;
    int expense_left; 
    for (int i = 0; i < arr.size(); i++){
        expense_left = m - arr[i]; // for every entry, calculate expense left
        auto search = find(arr.begin()+i+1, arr.end(), expense_left); // see if expense left is available
        
        //if expense left is available, return 1-based index
        if (search != arr.end()){
            result.push_back(i+1);
            result.push_back(search-arr.begin()+1); // search-arr.begin() gives 0-based indexing, so add 1
            break;
        }
    }
    return result;    
}