[LeetCode Python3] 396. Rotate Function + 暴力 + 错位相减

396. Rotate Function

暴力 时间复杂度O(n*n)

按照计算规则，一步一步来

class Solution:
    def maxRotateFunction(self, nums: List[int]) -> int:
        size, res = len(nums), -float('inf')
        for i in range(size):
            tmp = 0
            for j in range(size):
                tmp += j * nums[(j + size - i) % size]  # 用下标(j + size - i) % size来表示顺时针旋转i个位置
            res = max(res, tmp)
        return res

错位相减 时间复杂度O(2*n)

class Solution:
    def maxRotateFunction(self, nums: List[int]) -> int:
        size, nsum = len(nums), sum(nums)
        tmp = sum([i*nums[i] for i in range(size)])
        res = tmp
        for i in range(1, size):
            tmp = tmp + nsum - size * nums[size-i]
            res = max(res, tmp)
        return res