If it says O(1) space I can understand how to do that, but what does no "extra space" mean? If I use another integer to save the reversed number does it mean I'm still using extra space? Or when I simply am using an integer i for loop does it mean I have extra space?
Extra space here typically means O(n) space.
However I also misunderstood it and came up with a version with no extra 'variable':