More on KSubsets
- Subject: [mg2429] More on KSubsets
- From: wself at viking.emcmt.edu (Will Self)
- Date: Thu, 9 Nov 1995 04:41:42 GMT
- Approved: usenet@wri.com
- Distribution: local
- Newsgroups: wri.mathgroup
- Organization: Wolfram Research, Inc.
- Sender: daemon at wri.com ( )
Axel's question about KSubsets has some interesting variations.
For example, there is another possibly useful order on the k-subsets,
different from the lexicographic one. For a finite subset s of the non-negative integers, compute the number n such that the digits in the
binary representation for n corresponding to elements of s are 1, and the
rest of the digits are 0. For the set {0,1,3} the associated number would
be 2^0 + 2^1 + 2^3 = 11.
Now you can order the subsets s according to their associated numbers n.
It's no problem to create the function nthSubset, which gives the nth
subset in this ordering, but what about the function nthKSubset, which
for a given k would return the nth k-subset in this ordering? Anyone
have a nice way to do this?
Will Self