Sliding Window Maximum

Screen Shot 2017-09-13 at 16.42.48.png

public class Solution {
    public int[] maxSlidingWindow(int[] nums, int k) {
        if(nums == null || nums.length < k || k <= 0) return new int[0];
        int n = nums.length;
        int[] res = new int[n - k + 1];
        int ri = 0;
        Deque<Integer> deque = new LinkedList<>();
        for(int i = 0; i < n ; i++)
        {
            while(!deque.isEmpty() && deque.peekFirst() < i - k + 1) deque.pollFirst();
            while(!deque.isEmpty() && nums[deque.peekLast()] < nums[i]) deque.pollLast();
            deque.offerLast(i);
            if(i >= k - 1) res[ri++] = nums[deque.peekFirst()];
        }
        return res;
    }
}