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
>> >
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