package main

type Window struct {
	nums      []int
	begin     int
	end       int
	size      int
	numsCount int
}

func (w *Window) Next() *Window {
	if w.end+1 >= w.numsCount {
		return nil
	}
	w.begin++
	w.end++
	return w
}

func (w *Window) InWindow(index int) bool {
	return (index >= w.begin) && (index <= w.end)
}

func maxBruteForce(nums []int, begin int, end int) WindowMaximum {
	max := nums[begin]
	index := begin
	for i := begin + 1; i <= end; i++ {
		if nums[i] > max {
			max = nums[i]
			index = i
		}
	}

	return WindowMaximum{index: index, value: max, valid: true}
}

func (w *Window) Max(prevMax WindowMaximum) WindowMaximum {
	if !prevMax.valid {
		return maxBruteForce(w.nums, w.begin, w.end)
	}

	if (w.nums[w.begin-1] == w.nums[w.begin]) && (w.nums[w.end-1] == w.nums[w.end]) {
		return prevMax
	}

	if !w.InWindow(prevMax.index) {
		return maxBruteForce(w.nums, w.begin, w.end)
	}

	if w.nums[w.end] >= prevMax.value {
		return WindowMaximum{value: w.nums[w.end], valid: true, index: w.end}
	}

	return prevMax
}

func NewWindow(nums []int, k int) *Window {
	w := Window{}
	w.nums = nums
	w.size = k
	w.numsCount = len(nums)
	w.begin = 0
	w.end = k - 1

	if w.end < 0 {
		return nil
	}
	if k > w.numsCount {
		return nil
	}

	return &w
}

type WindowMaximum struct {
	index int
	value int
	valid bool
}

func MaxSlidingWindow(nums []int, k int) []int {
	maximums := []int{}
	var max WindowMaximum

	for w := NewWindow(nums, k); w != nil; w = w.Next() {
		max = w.Max(max)
		maximums = append(maximums, max.value)
	}

	return maximums
}