when you say "No less than Y people ahead" that means that in the best possible scenario (for Vasya) there are exactly Y people ahead of him

You need to consider that this scenario/position might not be possible at all because too many people would stand behind him in that case!

Because in such case, exception does not originate from inside of str. It's raised before str is executed.

That's the idea. Most of these Katas are 7 Kyu and can be solved easily in some languages. For instance, this Kata is trivial in Python, Ruby and Haskell. It's much more difficult in Java, cpp, JS, and others that don't have in-built cartesian product methods because you must use two nested loops correctly.

[-10, 10] should return -1. You start at index 0, and here the left sum is 0 and right sum is 10. Next, index is 1, and here left sum is -10 and right sum is zero. You never go to index 2 (where the left sum would equal the right sum), since index 2 is not an index in the array.

There's an implicit loop; the complexity is the same.

The log appears above the test result, you're confusing the expected value of one test with the input value of the next one, the test with that input expects "YES".

Not an issue, the first value is what your function returned, not the input value, for the first one, the input was "foobar99". If you want to see the input value, print it, it'll appear above the test result.

Read the description carefully, print the input and see what happens.

Timing out is not an issue.