Only 8 days into Ubunto, and I did some damage

Only 8 days into Ubunto, and I did some damage

In order to eliminate some of the permissions obstacles I keep finding, I
decided to make it easier on myself. I did
$ sudo chmod 755 -R /usr
If I knew 10 hours ago what I've learned in researching this, I wouldn't
have used that command. I tried this first
$ chmod 755 -R /usr
That resulted an a large number of these:
$ chmod: changing permissions of '/usr/dir/file': Operation not permitted
I tried another sudo command, and that one returns:
effective uid is not 0, is sudo installed setuid root?
Is there a way to reverse this without a clean reinstall? All I've done
for the last 8 or 9 days is to read, configure software, and try to learn
how to use the terminal, and I don't exactly look forward to starting that
process again, even if not quite back to the beginning.