Write alternating_sum(n) that returns 1 - 2 + 3 - 4 + 5 - ... continuing up to n. Odd numbers are added and even numbers are subtracted. For n = 0 return 0.
Examples
Input: n = 5
Output: 3
Explanation: 1 - 2 + 3 - 4 + 5 = 3
Input: n = 4
Output: -2
Constraints
0 <= n <= 10**5
Goals
- Alternate between two actions inside a loop
- Use the parity of the loop counter