suppose the slope of line on the x>0 is k ,and slope of (0,0) to n
points is k1,k2,...kn then intersection point of x1==1/(k1-k),x2=1/(k2-k)...xn=1/(kn-k)
then we choose (x4-x1)/(x2-x1)==(x4'-x1')/(x2'-x1') and (x3-x2)/(x3-x4)==（x3'-x2'）/(x3'-x4')
we multiply these two equations guess what happens, yes: k is offset
then we can get (k4-k1)*(k3-k2)/((k2-k1)*(k3-k4))==(k4'-k1')*(k3'-k2')/((k2'-k1')*(k3'-k4'))
en.. this convert to string matching prolems,so suffix array can solve it

Edited by author 26.10.2018 10:33