Divisible and Non-divisible Sums Difference

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Question

Approach

I calculated the total sum from 1 to n using the formula n * (n + 1) // 2. Then, I found how many numbers are divisible by m (n // m) and used the arithmetic series formula to get their sum. Finally, I subtracted the divisible sum from the total to get the difference between non-divisible and divisible sums.

Implementation

class Solution:
    def differenceOfSums(self, n: int, m: int) -> int:
        total_sum = n * (n + 1) // 2

        k = n // m

        divisible_sum = m * k * (k + 1) // 2

        return total_sum - 2 * divisible_sum

Complexities

• Time: O(1)
• Space: O(1)