Merge pull request #4 from yutingyw/prim

Prim's algorithm
Minor style fixup in ywprim.py
Merge pull request #5 from jeeyoungk/2014-06-16-jee-ywprime-minor-fixup

Minor style fixup in ywprim.py
Merge branch 'master' of github.com:jeeyoungk/jee-yuting-exercise