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Facebook Invite Challenge
Copyright (c) 2010  Peter Heinrich

When Facebook opened their Seattle office, they wanted to celebrate with an
open-house (recruiting) party in their new space.  Since space was limited,
however, they chose to limit invitations to those who could solve a little
puzzle they devised.

http://www.facebook.com/note.php?note_id=146727365346299

Actually, solutions to two puzzles were required, since the post above didn't
explicitly reveal the URL where details of the challenge could be found.  In-
stead, a partial URL was listed, with clues describing the last portion:

  http://www.facebook.com/seattle/[insert-word-here]

  The first occurrence of 'e' comes before 1 occurrence of 's'.
  The first occurrence of 'i' comes before 1 occurrence of 'n'.
  The first occurrence of 'i' comes before 1 occurrence of 'i'.
  The first occurrence of 'n' comes before 2 occurrences of 'e'.
  The first occurrence of 'e' comes before 1 occurrence of 'e'.
  The first occurrence of 'i' comes before 1 occurrence of 'v'.
  The first occurrence of 'n' comes before 1 occurrence of 'i'.
  The first occurrence of 'n' comes before 1 occurrence of 'v'.
  The first occurrence of 'i' comes before 1 occurrence of 's'.
  The first occurrence of 't' comes before 1 occurrence of 's'.
  The first occurrence of 'v' comes before 1 occurrence of 's'.
  The first occurrence of 'v' comes before 2 occurrences of 'e'.
  The first occurrence of 't' comes before 2 occurrences of 'e'.
  The first occurrence of 'i' comes before 2 occurrences of 'e'.
  The first occurrence of 'v' comes before 1 occurrence of 't'.
  The first occurrence of 'n' comes before 1 occurrence of 't'.
  The first occurrence of 'v' comes before 1 occurrence of 'i'.
  The first occurrence of 'i' comes before 1 occurrence of 't'.
  The first occurrence of 'n' comes before 1 occurrence of 's'.

I'm not much for word games or anagrams (actually, I hate them), so I wasn't
interested in puzzling through this--maybe it was straightforward, I don't
know.  Instead, I took the easy way:

peter@Ancaeus ~ $ aspell dump master > dict.txt
peter@Ancaeus ~ $ egrep "[^s]*e.*s" dict.txt | egrep "[^n]*i.*n" | egrep "^([^i]*i[^i]*){2}" | egrep "[^n]*n[^e]*e[^e]*e" | egrep "^([^e]*e[^e]*){2}$" | egrep "[^v]*i.*v" | egrep "[^n]*n.*i" | egrep "[^n]*n.*v" | egrep "[^i]*i.*s" | egrep "[^t]*t.*s" | egrep "[^v]*v.*s" | egrep "[^v]*v[^e]*e[^e]*e" | egrep "[^t]*t[^e]*e[^e]*e" | egrep "[^i]*i[^e]*e[^e]*e" | egrep "[^v]*v.*t" | egrep "[^n]*n.*t" | egrep "[^v]*v.*i" | egrep "[^i]*i.*t" | egrep "[^n]*n.*s"
invitees
vindictiveness
vindictiveness's

Not pretty, but straightforward, since the regexes can basically be copied
directly from the individual clues.  Only three words satisfied all the con-
straints, and it seemed pretty clear which was intended.

I subsequently refined the expression, since the clues make it clear that:

  1. only the letters e, i, n, s, t, and v appear in the word
  2. the letter s appears exactly once, at the end
  3. the letters e and i appear exactly twice

peter@Ancaeus ~ $ aspell dump master | egrep "^[eintv]{7,}s$" | egrep "n.*e{2}" | egrep "v.*e{2}"
invitees

With the URL cracked, the real programming challenge was revealed: use the
Facebook Graph API to determine which of your friends shared the most likes and
interests with you.  I think most people would agree that this was almost too
easy, since (as I discovered) Facebook's Graph API makes this kind of thing a
snap.