【重点】【滑动窗口】239. 滑动窗口最大值

题目
也可参考：剑指offer——面试题65：滑动窗口的最大值

class Solution {
    public int[] maxSlidingWindow(int[] nums, int k) {
        int[] res = new int[nums.length - k + 1];
        Deque<Integer> q = new LinkedList<>();
        int inx = 0;
        while (inx < k) {
            if (q.isEmpty()) {
                q.offerLast(nums[inx++]);
            } else {
                while (!q.isEmpty() && q.peekLast() < nums[inx]) {
                    q.pollLast();
                }
                q.offerLast(nums[inx++]);
            }
        }
        res[0] = q.peekFirst(); // inx - k
        while (inx < nums.length) {
            int d = nums[inx - k];
            if (q.peekFirst() == d) {
                q.pollFirst();
            }
            while (!q.isEmpty() && q.peekLast() < nums[inx]) {
                q.pollLast();
            }
            q.offerLast(nums[inx++]);
            res[inx - k] = q.peekFirst();
        }

        return res;
    }
}