Every entry of factors is a non-zero integer. Count the non-empty contiguous stretches whose product is positive. The product itself can be enormous, so do not compute it.
Examples
Input: factors = [2, -3, -1, 4]
Output: 6
Explanation: [2], [2, -3, -1], [2, -3, -1, 4], [-3, -1], [-3, -1, 4] and [4].
Input: factors = [-5]
Output: 0
Constraints
1 <= len(factors) <= 10**5-10**9 <= factors[i] <= 10**9,factors[i] != 0- Target complexity: O(n) time, O(1) extra space.
Goals
- Reduce a product's sign to the parity of negative factors
- Count equal-parity prefix pairs with two counters