There is a nuanced mistake in

> If your machine runs out of memory, reversed[i] will cause a segfault upon being accessed. In order to avoid unhelpful segfaults, the program should check for a null pointer and gracefully exit if one is found

If overcommit is enabled (often by default), malloc will not return null when machine runs out of memory. malloc will still return null if input argument is invalid (e.g. too large).