239-sliding-window-maximum

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]

My solution：

class Solution(object):
    def maxSlidingWindow(self, nums, k):
        """
        :type nums: List[int]
        :type k: int
        :rtype: List[int]
        """
        maxList = []
        stack = []
        maxNum = float('-inf')
        for i in range(k):
            stack.append(nums[i])
            maxNum = maxNum if nums[i] <= maxNum else nums[i]
        maxList.append(max(stack))

        i = k

        while i < len(nums):
            out_num = stack.pop(0)
            in_num = nums[i]
            stack.append(in_num)
            if out_num == maxList[-1]:
                maxList.append(max(stack))
            else:
                bigger_num = max(in_num,maxList[-1])
                maxList.append(bigger_num)
            i += 1
            
        return maxList
            

Sadly it’s out of time limit. It must because of the max function.

Time Complexity: O(n*k) Space Complexity: O(n+k)

Best solution：

Use a supportive quene which is in a decrease sort.

from collections import deque
class MyQueue():
    def __init__(self):
        self.queue = deque()
    def push(self,value):
        while self.queue and value > self.queue[-1]:
            self.queue.pop()
        self.queue.append(value)
    def pop(self,value):
        if self.queue and value == self.queue[0]:
            self.queue.popleft()

    def front(self):
        return self.queue[0]

class Solution(object):
    
    def maxSlidingWindow(self, nums, k):
        """
        :type nums: List[int]
        :type k: int
        :rtype: List[int]
        """
        que = MyQueue()
        result = []
        for i in range(k): #先将前k的元素放进队列
            que.push(nums[i])
        result.append(que.front()) #result 记录前k的元素的最大值
        for i in range(k, len(nums)):
            que.pop(nums[i - k]) #滑动窗口移除最前面元素
            que.push(nums[i]) #滑动窗口前加入最后面的元素
            result.append(que.front()) #记录对应的最大值
        return result
            

Time Complexity: O(n) Space Complexity: O(k)