Count the non-empty contiguous windows of nums whose product is even. The product itself may be astronomically large, so you must not compute it.
Examples
Input: nums = [1, 2, 3]
Output: 4
Explanation: [2], [1, 2], [2, 3], [1, 2, 3] are even; [1], [3] are odd.
Input: nums = [1, 3, 5]
Output: 0
Constraints
0 <= len(nums) <= 10**5-10**9 <= nums[i] <= 10**9(0 counts as even)- Target complexity: O(n) time.
Goals
- Count the complement (all-odd windows) instead of the target directly
- Turn a run of length L into L*(L+1)/2 windows