maxSlidingWindow.swift

class Solution {
    var deque: [Int] = []
    var nums: [Int]! = []
    
    func cleanDeque(_ i: Int, _ k: Int) {
        if deque.isEmpty == false{
            if let first = deque.first, first == i - k {
                deque.removeFirst()
            }
        }

        while deque.isEmpty == false {
            if let last = deque.last, nums[i] > nums[last] {
                deque.removeLast()
            }else {
                break
            }
        }

    }
    
    func maxSlidingWindow(_ numsa: [Int], _ k: Int) -> [Int] {
        nums = numsa
        let len = nums.count
        if len * k == 0 { return [] }
        if k == 1 { return nums }

        var maxId = 0
        for i in 0..<k {
            cleanDeque(i, k)
            deque.append(i)
            if nums[i] > nums[maxId] { maxId = i }
        }
        var output: [Int] = []
        output.append(nums[maxId])
        for i in k..<len {
            cleanDeque(i, k)
            deque.append(i)
            if let first = deque.first {
            output.append(nums[first])
            }
        }
        return output
    }
}