On test #22,we can extend two segments and get two valid circles,which circle do we choose
??

Maybe there are some error in my code...
seems there can only be one circle..

Edited by author 30.11.2016 13:28

Spend one day for a typing error:

  alpha=atan2(y4-y3,x4-y3)+pi/2.;

it's 作死 for Chinese