A lot of novice C++ programmers learn about std::vector, that it basically works like an automatically growing array, and stop right there. Later, they only lookup its documentation in order to see how to do very specific things, for example, removing items. Using STL containers like this will only scratch the surface of how much they help writing clean, maintainable, and fast code.
This section is all about removing items from in-between a vector instance. When an item disappears from a vector, and sits somewhere in the middle between other items, then all items right from it must move one slot to the left (which gives this task a runtime cost within O(n)). Many novice programmers will do that using a loop, since it is also not really a hard thing to do. Unfortunately, they will potentially ignore a lot...
