[第二輪]4/8-4/14 CareerCup 7.3

7.3 Given two lines on a Cartesian plane, determine whether the two lines would intersect.

发帖规范:

http://www.1point3acres.com/bbs/thread-48094-1-1.html

http://www.1point3acres.com/bbs/thread-32423-1-1.html

用叉乘做跨立检测，
https://code.google.com/p/leet-algorithm/source/browse/trunk/CareerCup5/7/7.3.cpp