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]

Example 3:

Input: nums = [1,-1], k = 1

Output: [1,-1]

Example 4:

Input: nums = [9,11], k = 2

Output: [11]

Example 5:

Input: nums = [4,-2], k = 2

Output: [4]

Constraints:

Solution

# @param {Integer[]} nums
# @param {Integer} k
# @return {Integer[]}
def max_sliding_window(nums, k)
  n = nums.length
  res = []
  x = 0
  dq = []
  i = 0
  j = 0

  while j < n
    while !dq.empty? && dq.last < nums[j]
      dq.pop
    end

    dq.push(nums[j])

    if j - i + 1 == k
      res[x] = dq.first
      x += 1

      if dq.first == nums[i]
        dq.shift
      end

      i += 1
    end

    j += 1
  end

  res
end