Given a list nums, consider every contiguous window whose length is odd (1, 3, 5, ...). Return the sum of the sums of all such windows.
Examples
Input: nums = [1, 4, 2, 5]
Output: 30
Explanation: length 1 windows total 12; length 3 windows [1,4,2] = 7 and [4,2,5] = 11; 12 + 7 + 11 = 30.
Input: nums = [3]
Output: 3
Constraints
1 <= len(nums) <= 10**5-1000 <= nums[i] <= 1000- Target complexity: O(n) time. Enumerating the windows is O(n^2) and too slow for the largest tests.
Goals
- Replace enumeration of windows by counting how often each element is used
- Derive the number of odd-length windows through a position