239. 滑动窗口最大值

    public int[] maxSlidingWindow(int[] nums, int k) {
        // 改为大顶堆
        PriorityQueue<int[]> queue = new PriorityQueue<>(k, new Comparator<int[]>() {
            @Override
            public int compare(int[] o1, int[] o2) {
                return o2[0] - o1[0];
            }
        });
        int[] ans = new int[nums.length - k + 1];
        for (int i = 0; i < k; i++) {
            // queue's element 0:值 1:值对应的索引
            queue.offer(new int[]{nums[i], i});
        }
        ans[0] = queue.peek()[0];
        for (int i = k; i < nums.length; i++) {
            queue.offer(new int[]{nums[i], i});
            // 索引值
            while (queue.peek()[1] <= i - k) {
                // 最大顶堆值不在滑动窗口内
                queue.poll();
            }
            ans[i - k + 1] = queue.peek()[0];
        }
        return ans;
    }

    public int[] maxSlidingWindow(int[] nums, int k) {
        int n = nums.length;
        if (n == 0) {
            return nums;
        }
        // 队列存索引值
        Deque<Integer> deque = new LinkedList();
        int[] ans = new int[n - k + 1];
        for (int i = 0; i < n; i++) {
            // i-k+1 滑动窗口起始索引值
            if (!deque.isEmpty() && deque.peek() < i - k + 1) {
                deque.poll();
            }
            // nums[i]比队列中的元素都大
            while (!deque.isEmpty() && nums[i] >= nums[deque.peekLast()]) {
                deque.pollLast();
            }
            deque.offer(i);
           // i-k+1>=0 读完滑动窗口所有值
            if (i - k + 1 >= 0) {
                ans[i - k + 1] = nums[deque.peek()];
            }
        }
        return ans;
    }