Sliding Window Maximum

 Sliding Window Maximum

Given an array num, there is a sliding window of size k which is moving from the very left of the array to the very right. You can only see the k numbers in the window. Each time the sliding window moves right by one position. Return the max sliding window.

Follow up:
Could you solve it in linear time?

Example:

Input: nums = [1,3,-1,-3,5,3,6,7], and k = 3
Output: [3,3,5,5,6,7] 
Explanation: 

Window position                Max
---------------               -----
[1  3  -1] -3  5  3  6  7       3
 1 [3  -1  -3] 5  3  6  7       3
 1  3 [-1  -3  5] 3  6  7       5
 1  3  -1 [-3  5  3] 6  7       5
 1  3  -1  -3 [5  3  6] 7       6
 1  3  -1  -3  5 [3  6  7]      7

 

Constraints:

• 1 <= nums.length <= 10^5
• -10^4 <= nums[i] <= 10^4
• 1 <= k <= nums.length

class Solution {

public:

    vector<int> maxSlidingWindow(vector<int>& nums, int k) {

        int n=nums.size();

        if(n<k) return {};

         deque<int> dq;

        vector<int> ans;

        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>=k-1) ans.push_back(nums[dq.front()]);

        }

        return ans;

    }

};