239. Sliding Window Maximum

Given an array nums, 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.

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

Note:
You may assume k is always valid, 1 ≤ k ≤ input array's size for non-empty array.

Follow up:
Could you solve it in linear time?

public class Solution {
    public int[] maxSlidingWindow(int[] nums, int k) {
        int n = nums.length;
        if (n == 0) {
            return nums;
        }
        int[] result = new int[n - k + 1];
        LinkedList<Integer> dq = new LinkedList<>();
        for (int i = 0; i < n; i++) {
            if (!dq.isEmpty() && dq.peek() < i - k + 1) {
                dq.poll();
            }
            while (!dq.isEmpty() && nums[i] >= nums[dq.peekLast()]) {
                dq.pollLast();
            }
            dq.offer(i);
            if (i - k + 1 >= 0) {
                result[i - k + 1] = nums[dq.peek()];
            }
        }
        return result;
    }
}