131 reputation
4
bio website bit-kit.com
location Oslo, Norway
age 38
visits member for 3 years, 9 months
seen Dec 11 '13 at 4:57

Programmer from Oslo, Norway, with a keen interest in math.


May
6
awarded  Supporter
Jan
30
awarded  Teacher
Jan
30
comment Finding points in a grid with exactly k paths to them?
Sigh... Please read my answer thoroughly before you answer. Finding all i and j such as i!/((i-j)!j!)=n will take O(n). It's a simple loop, from 0 to max(i, j).
Jan
29
comment Finding points in a grid with exactly k paths to them?
Did you read my entire answer? If there are R right moves and U up moves between two points, then all paths leading between them will number C(R+U, R) (using binomial notation). Thus one will need to iterate over i and j to find all of them that result in i!/((i-j)!j!)=n. From there one can use my proposition in the second last paragraph to calculate the actual paths, given that you now know the steps that can take you there (but not the order).
Jan
29
comment Finding points in a grid with exactly k paths to them?
Expanded the solution based on your comments.
Jan
29
comment Finding points in a grid with exactly k paths to them?
If you start at (0,0), I get that you have 15 possible paths to (4,2), and 7 possible paths to (6,1) or have I misunderstood the question...?
Jan
29
comment Finding points in a grid with exactly k paths to them?
Sure you do! Between (x,y) and (x+3,y+3) there are exactly 3 'U's and 3 'R's. Any (new) combination of R, R, R, U, U and U will give a new path.
Jan
29
answered Finding points in a grid with exactly k paths to them?
Jan
14
awarded  Student
Jan
14
comment Creating a parametrized ellipse at an angle
Thanks! I'll try this out in code tomorrow.
Jan
14
comment Creating a parametrized ellipse at an angle
Yep, Isaac is correct. it would produce the same looking ellipse since t is in the interval [0, 360], regardless of whether a constant is added. Your answer would simply start and end the ellipse at a different place along the curve.
Jan
14
awarded  Autobiographer
Jan
14
asked Creating a parametrized ellipse at an angle