Sliding Window Maximum.cpp

class Solution {
public:
    vector<int> maxSlidingWindow(vector<int>& nums, int k) {
        int len = nums.size();
        deque<int> dq;
        vector<int> res;
        for(int i = 0; i < len; ++i)
        {
            while(dq.size() && nums[dq.back()] <= nums[i])
                dq.pop_back();
            dq.push_back(i);
            while(dq.size() && dq.front() <= i - k)
                dq.pop_front();

            if(i >= k - 1 && k)
                res.push_back(nums[dq.front()]);
        }
        return res;
    }
};