This was a programming assignment as part of a job interview.

The goal is to handle a simple package dependency manager, perhaps similar to Bundler.  Dependencies are maintained, installed as needed, and removed when no longer needed unless those same packages were installed explicitly

Commands:

DEPEND parent child1 [child2...]
  parent depends on children
INSTALL package
  installs the given package and those on which it depends
REMOVE package
  removes the given package and those on which it depends, unless they are required by other packages or were installed explicitly
LIST
  lists installed packages
END
  ends execution and exits

Example Input
DEPEND   ALFA BRAVO CHARLIE
DEPEND BRAVO CHARLIE
DEPEND DELTA BRAVO CHARLIE
DEPEND  ECHO   BRAVO  FOXTROT
INSTALL CHARLIE
INSTALL ALFA
INSTALL GOLF
REMOVE CHARLIE
INSTALL ECHO
INSTALL DELTA
LIST
REMOVE ALFA
REMOVE CHARLIE
REMOVE DELTA
REMOVE CHARLIE
INSTALL CHARLIE
REMOVE BRAVO
REMOVE ECHO
REMOVE BRAVO
LIST
END


Output for the Example Output
DEPEND   ALFA BRAVO CHARLIE
DEPEND BRAVO CHARLIE
DEPEND DELTA BRAVO CHARLIE
DEPEND  ECHO   BRAVO  FOXTROT
INSTALL CHARLIE
  Installing CHARLIE
INSTALL ALFA
  Installing BRAVO
  Installing ALFA
INSTALL GOLF
  Installing GOLF
REMOVE CHARLIE
  CHARLIE is still needed.
INSTALL ECHO
  Installing FOXTROT
  Installing ECHO
INSTALL DELTA
  Installing DELTA
LIST
  FOXTROT
  ECHO
  DELTA
  CHARLIE
  GOLF
  BRAVO
  ALFA
REMOVE ALFA
  Removing ALFA
REMOVE CHARLIE
  CHARLIE is still needed.
REMOVE DELTA
  Removing DELTA
REMOVE CHARLIE
  CHARLIE is still needed.
INSTALL CHARLIE
  CHARLIE is already installed.
REMOVE BRAVO
  BRAVO is still needed.
REMOVE ECHO
  Removing ECHO
  Removing FOXTROT
  Removing BRAVO
REMOVE BRAVO
  BRAVO is not installed.
LIST
  CHARLIE
  GOLF
END