Maximum of all subarrays of size k

vector <int> max_of_subarrays(int *arr, int n, int k){
    deque<int> Qi(k);
    vector<int> ans;
    int i;
    for (i = 0; i < k; ++i) {
        while ((!Qi.empty()) && arr[i] >= arr[Qi.back()])
            Qi.pop_back();
        Qi.push_back(i);
    }
    for (; i < n; ++i){
        ans.push_back(arr[Qi.front()]);
        while ((!Qi.empty()) && Qi.front() <= i - k)
            Qi.pop_front(); 
        while ((!Qi.empty()) && arr[i] >= arr[Qi.back()])
            Qi.pop_back();
 
        Qi.push_back(i);
    }
    ans.push_back(arr[Qi.front()]);
    return ans;
}