Sum numbers from 1 to n

Write a function that returns the sum of all integers from 1 to n inclusive.

sum loop arithmetic function

Write a function `sum_to_n(n)` that takes an integer `n` and returns the sum of all integers from 1 to n inclusive. For example, `sum_to_n(5)` returns `1 + 2 + 3 + 4 + 5 = 15`. Assume `n` is a non-negative integer (n >= 0). If `n` is 0, return 0. Use a loop or arithmetic formula.

Constraints

0 <= n <= 1000. The function should handle integers within this range efficiently. Time complexity: O(n) or O(1).

Example

>>> sum_to_n(5)
15
>>> sum_to_n(0)
0
>>> sum_to_n(10)
55

5 points ~5 min

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Hints

Remember to handle the case when n is 0.

You can use a for loop with range(1, n+1).

The arithmetic formula n*(n+1)//2 is also valid.

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