• Sliding Window Maximum

vector<int> maxSlidingWindow(vector<int>& nums, int k) {
        vector<int> res;
        deque<int> dq;
        for(int i=0;i<nums.size();i++){
            if(!dq.empty()&&dq.front()==i-k){
                dq.pop_front();
            }
            while(!dq.empty()&&nums[dq.back()]<nums[i]){
                 dq.pop_back();
            }
            dq.push_back(i);
            if(i+1>=k){
                res.push_back(nums[dq.front()]); 
            }
        }
        return res;
    }