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
func maxSlidingWindow(nums []int, k int) []int {
if k == 1 {
return nums
}
i := 1
prev := nums
var reuse []int
for ; (1 << i) <= k; i++ {
next := maxReduce(prev, 1<<(i-1), reuse)
reuse = prev
prev = next
}
if 1<<i == k {
return prev
}
diff := k - (1 << (i - 1))
return maxReduce(prev, diff, nil)[:len(nums)-k+1]
}
func maxReduce(nums []int, skip int, reuse []int) []int {
// reuse allows to reuse prior allocations
n := len(nums)
var result []int
if reuse != nil {
result = reuse
} else {
result = make([]int, n-skip)
}
for i := 0; i < n-skip; i++ {
result[i] = max(nums[i], nums[i+skip])
}
return result[:n-skip]
}