滑动窗口求最大值 leetcode 59

滑动窗口最大值问题
利用递减队列实现
Dequeue dequeue = new LinkedList<>();
递减队列方法说明
peekFirst获取队头元素
pollFirsr队头元素出队
offerLast == add在队尾插入新元素

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