Sure, the growth of the list itself is not quadratic, but the allocations of the new objects (the {} part) invokes a GC every K iterations, and a naive, stop-th

Sure, the growth of the list itself is not quadratic, but the allocations of the new objects (the {} part) invokes a GC every K iterations, and a naive, stop-the-world, mark-and-sweep GC is O(n) in number of live objects.