@Dave I was wrong. It can't be done in O(n^2) time. The best we can do is sort each row like you suggested in your other post. That will still be O((n^2)logn).
Thanks, - Ravindra On Sun, Oct 24, 2010 at 7:06 PM, Meng Yan <mengyan.fu...@gmail.com> wrote: > for the 3th step, > for i=1 to n > for j=i+1 to n > for k=j+1 to n > compare A[i,j] and A[j,k] > if A[i,j]==A[j,k] > find i,j,k are collinear. > > so we should need O(n^3), is it right? > > On Sun, Oct 24, 2010 at 1:05 AM, ravindra patel > <ravindra.it...@gmail.com>wrote: > >> Can be done in O(n^2) time using the slope as people suggested above. >> >> 1- Sort the points in increasing order of x cord. O(nlogn) >> 2- prepare a n*n matrix A where A[i,j] = slope( point(i), point(j) ) - >> O(n^2) [Note that point i and j are sorted in increasing order of x] >> 3- find a pair of A[i,j] and A[j,k] with same slope. [Can be done in >> O(n^2)] >> >> Thanks, >> - Ravindra >> >> >> On Sun, Oct 24, 2010 at 10:11 AM, Dave <dave_and_da...@juno.com> wrote: >> >>> @Preetika: Then you have to look for duplicates in an array of n(n-1)/ >>> 2 real numbers. I think this takes the complexity above O(n^2). >>> >>> Dave >>> >>> On Oct 23, 10:54 pm, preetika tyagi <preetikaty...@gmail.com> wrote: >>> > You have to scan every pair of points only once to get the value of 'm' >>> and >>> > 'a', so the time complexity would be O(n^2). >>> > >>> > >>> > >>> > On Sat, Oct 23, 2010 at 6:22 PM, Meng Yan <mengyan.fu...@gmail.com> >>> wrote: >>> > > there are (n*(n-1))/2pairs of points. I think if we use your method, >>> the >>> > > time complexity should be O(n^4). >>> > >>> > > Is it possible to put all points into k different domain and using >>> > > T(n)=T(n/k)+f(n) to solve this problem? >>> > >>> > > On Sat, Oct 23, 2010 at 7:51 PM, preetika tyagi < >>> preetikaty...@gmail.com>wrote: >>> > >>> > >> Is there any specific need to use recursion? >>> > >>> > >> One alternate is to find slope and constant (m and c) for every pair >>> of >>> > >> points and same value of m & c will specify the points on the same >>> line. >>> > >> Time complexity is O(n*n). >>> > >>> > >> On Sat, Oct 23, 2010 at 4:31 PM, Meng Yan <mengyan.fu...@gmail.com >>> >wrote: >>> > >>> > >>> Given n point on the plane, find out whether any 3point on the same >>> > >>> line. >>> > >>> > >>> How to use recursion to solve the problem? Could you help me find >>> the >>> > >>> algorithm and give the time complexity? >>> > >>> > >>> Bests, >>> > >>> Claire >>> > >>> > >>> -- >>> > >>> You received this message because you are subscribed to the Google >>> Groups >>> > >>> "Algorithm Geeks" group. >>> > >>> To post to this group, send email to algoge...@googlegroups.com. >>> > >>> To unsubscribe from this group, send email to >>> > >>> algogeeks+unsubscr...@googlegroups.com<algogeeks%2bunsubscr...@googlegroups.com> >>> <algogeeks%2bunsubscr...@googlegroups.com> >>> > >>> . >>> > >>> For more options, visit this group at >>> > >>>http://groups.google.com/group/algogeeks?hl=en. >>> > >>> > >> -- >>> > >> You received this message because you are subscribed to the Google >>> Groups >>> > >> "Algorithm Geeks" group. >>> > >> To post to this group, send email to algoge...@googlegroups.com. >>> > >> To unsubscribe from this group, send email to >>> > >> algogeeks+unsubscr...@googlegroups.com<algogeeks%2bunsubscr...@googlegroups.com> >>> <algogeeks%2bunsubscr...@googlegroups.com> >>> > >> . >>> > >> For more options, visit this group at >>> > >>http://groups.google.com/group/algogeeks?hl=en. >>> > >>> > > -- >>> > > You received this message because you are subscribed to the Google >>> Groups >>> > > "Algorithm Geeks" group. >>> > > To post to this group, send email to algoge...@googlegroups.com. >>> > > To unsubscribe from this group, send email to >>> > > algogeeks+unsubscr...@googlegroups.com<algogeeks%2bunsubscr...@googlegroups.com> >>> <algogeeks%2bunsubscr...@googlegroups.com> >>> > > . >>> > > For more options, visit this group at >>> > >http://groups.google.com/group/algogeeks?hl=en.- Hide quoted text - >>> > >>> > - Show quoted text - >>> >>> -- >>> You received this message because you are subscribed to the Google Groups >>> "Algorithm Geeks" group. >>> To post to this group, send email to algoge...@googlegroups.com. >>> To unsubscribe from this group, send email to >>> algogeeks+unsubscr...@googlegroups.com<algogeeks%2bunsubscr...@googlegroups.com> >>> . >>> For more options, visit this group at >>> http://groups.google.com/group/algogeeks?hl=en. >>> >>> >> -- >> You received this message because you are subscribed to the Google Groups >> "Algorithm Geeks" group. >> To post to this group, send email to algoge...@googlegroups.com. >> To unsubscribe from this group, send email to >> algogeeks+unsubscr...@googlegroups.com<algogeeks%2bunsubscr...@googlegroups.com> >> . >> For more options, visit this group at >> http://groups.google.com/group/algogeeks?hl=en. >> > > -- > You received this message because you are subscribed to the Google Groups > "Algorithm Geeks" group. > To post to this group, send email to algoge...@googlegroups.com. > To unsubscribe from this group, send email to > algogeeks+unsubscr...@googlegroups.com<algogeeks%2bunsubscr...@googlegroups.com> > . > For more options, visit this group at > http://groups.google.com/group/algogeeks?hl=en. > -- You received this message because you are subscribed to the Google Groups "Algorithm Geeks" group. 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