I think that the cast as int invalidated this solution

You are right, then just need to add an if or use the max function to have a lower bound.

Because when you remove two items ,it can only affects the surrouding items (old left and old right). While here they start searching from the beginning of the list.

For example if you have N, N, N, N, E, W, S when you delete E and W you dont need to go to the beginning but at the last N which was the left of the removed items.

I think that the second i = 1 at line 6 can be replaced by i -= 1

thanks for reporting issue, I added the random tests.