# Clojure: Выбор векторов

Когда использовать вектора, если есть списки? Достаточно знать ответы на несколько вопросов, если мы часто обращаемся к случайному элементу структуры данных и редко в нее что-либо добавляем, то векторы (массивы) будут правильным вариантом, если же мы динамически добавляем элементы в структуру данных и нам не так важна скорость получения случайного элемента, тогда можно использовать списки.

## Instructions

Реализуйте функцию `sum`, которая суммирует все элементы вектора.
Примеры:

``````(sum [])         ; => 0
(sum [10 -20])   ; => -10
(sum [1 2 3 4])  ; => 10
``````
The exercise doesn't pass checking. What to do? 😶

• Be sure to attach the test output, without it it's almost impossible to figure out what went wrong, even if you show your code. It's complicated for developers to execute code in their heads, but having a mistake before their eyes most probably will be helpful.
In my environment the code works, but not here 🤨

Tests are designed so that they test the solution in different ways and against different data. Often the solution works with one kind of input data but doesn't work with others. Check the «Tests» tab to figure this out, you can find hints at the error output.

My code is different from the teacher's one 🤔

It's fine. 🙆 One task in programming can be solved in many different ways. If your code passed all tests, it complies with the task conditions.

In some rare cases, the solution may be adjusted to the tests, but this can be seen immediately.

I've read the lessons but nothing is clear 🙄

It's hard to make educational materials that will suit everyone. We do our best but there is always something to improve. If you see a material that is not clear to you, describe the problem in “Discussions”. It will be great if you'll write unclear points in the question form. Usually, we need a few days for corrections.

By the way, you can participate in courses improvement. There is a link below to the lessons course code which you can edit right in your browser.

## Tips

If you got stuck and don't know what to do, you can ask a question in our huge and friendly community