LeetCode-in-All
239. Sliding Window Maximum
Hard
You are given an array of integers 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 1:
Input: nums = [1,3,-1,-3,5,3,6,7], 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
Example 2:
Input: nums = [1], k = 1
Output: [1]
Constraints:
1 <= nums.length <= 105-104 <= nums[i] <= 1041 <= k <= nums.length
Solution
defmodule Solution do
@spec max_sliding_window(nums :: [integer], k :: integer) :: [integer]
def max_sliding_window(nums, k) do
Enum.with_index(nums)
|> Enum.map_reduce(:queue.new(), fn {x, i}, q ->
enqueue(q, x, i)
|> get_max(i - k)
end)
|> elem(0)
|> Enum.drop(k - 1)
end
defp enqueue(q, x, i) do
case :queue.peek_r(q) do
{:value, {y, _}} when y <= x ->
:queue.drop_r(q)
|> enqueue(x, i)
_ -> :queue.in({x, i}, q)
end
end
defp get_max(q, drop_until) do
case :queue.peek(q) do
{:value, {_, j}} when j <= drop_until ->
:queue.drop(q)
|> get_max(drop_until)
{:value, {y, _}} -> {y, q}
end
end
end