[superrad]

When you reallocate your array you will in memory have your old array and your new larger array while you move your data over. At the very least you're using 2x and the extra memory for your expansion.

For your other points if you'd mentioned them in the interview you'd probably have been better received. Copying is really only that fast for POD objects (your objects copy constructors may need to do reallocation themselves or worse) so if you're suggesting a general solution you should be aware of that (or at least mention move constructors if they were available at the time) .

I would be surprised if any of the games you worked on actually shipped with an amortised resize of dynamic arrays (at least not for anything that didn't matter in the first place) so I don't know why you'd suggest it as a general solution in a game dev context.

[btilly]

A linked list needs a pointer for every piece of data. If the data is small, this will also be a 2-fold memory impact. Plus impacts on cache coherency.

[hnfong]

A typical C implementation would be using realloc():

The realloc() function tries to change the size of the allocation pointed to by ptr to size, and returns ptr. If there is not enough room to enlarge the memory allocation pointed to by ptr, realloc() creates a new allocation, copies as much of the old data pointed to by ptr as will fit to the new allocation, frees the old allocation, and returns a pointer to the allocated memory.

Worst case definitely 2x memory. But not necessarily always.