leetcode 239. Sliding Window Maximum

239. Sliding Window Maximum

Given an array 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.

For example,
Given nums = [1,3,-1,-3,5,3,6,7], and k = 3.

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

Therefore, return the max sliding window as [3,3,5,5,6,7].

最原始方法：自己求max

class Solution(object):
    def maxSlidingWindow(self, nums, k):
        """
        :type nums: List[int]
        :type k: int
        :rtype: List[int]
        """
     
        maxlist = []
        if k == 0:
            return maxlist
        if k > 0:
            length = len(nums)-k+1
            for j in range(0,length):
                max = nums[0+j]
                for i in range(0+j,k+j):
                    if nums[i] > max:
                        max = nums[i]
                print max
                maxlist.append(max)
            return maxlist

方法一：采取maxlist.append()，改进利用list的max函数求max

class Solution(object):
    def maxSlidingWindow(self, nums, k):
        """
        :type nums: List[int]
        :type k: int
        :rtype: List[int]
        """
     
        maxlist = []
        
        if k > 0:
            length = len(nums)-k+1
            for j in range(0,length):
                eachmax = max(nums[0+j:k+j]) 
                maxlist.append(eachmax)
            return maxlist
        if k == 0:
            return maxlist

        
        

s = Solution()
nums = [1,3,-1,-3,5,3,6,7]
k = 3
print s.maxSlidingWindow(nums,k)

方法二：再次改进。

class Solution(object):
    def maxSlidingWindow(self, nums, k):
        """
        :type nums: List[int]
        :type k: int
        :rtype: List[int]
        """
     
        if not nums:
            return []
        maxlist = [0]*(len(nums)-k+1)
        if k > 0:
            length = len(nums)-k+1
            for j in range(0,length):
                eachmax = max(nums[0+j:k+j]) 
                maxlist[j] = eachmax
            return maxlist


s = Solution()
nums = [1,3,-1,-3,5,3,6,7]
k = 3
print s.maxSlidingWindow(nums,k)

方法三：时间最短，别人的

class Solution(object):
    def maxSlidingWindow(self, nums, k):
        """
        :type nums: List[int]
        :type k: int
        :rtype: List[int]
        """
        if not nums:
            return []
        
        highest = max(nums[:k])
        ans = [0]*(len(nums)-k+1)
        ans[0] = highest
        last = nums[0]
        
        for i in range(1, len(nums)-k+1):
            if highest == last:
                highest = max(nums[i:i+k])
            elif nums[i+k-1] >= highest:
                highest = nums[i+k-1]
            
            ans[i] = highest
            last = nums[i]
            
        return ans