124.c: temp file
124.c: done

While extends the point(x,y) to a line (-border,y)(x,y), it fails
on test 15. Maybe there are two lines like this (x0,y)(x1,y) and
(x1,y)(x2,y).
After changed it to extends towards right. All test passed.
Maybe there is a protential bug in my code. T.T