[R] Help to write the R-code, please
Richard O'Keefe
r@oknz @end|ng |rom gm@||@com
Fri Dec 6 00:18:50 CET 2019
This particular task is not a problem about R.
It is a problem n combinatorics.
Start with the obvious brute force algorithm
(1) Let S be the union of all the sets
(2) For each K in 0 .. |S|
(3) Enumerate all |S| choose K subsets C of S
(4) If C satisfies the condition, report it and stop
(5) Report that there is no solution.
There is a function 'combn' in the 'combinat' package that
is perfectly suited to step 3.
I have not examined your outlined solution. Even if it is right,
it pays to START by writing a crude obvious brute force
algorithm like this so that you can test your test cases.
On Fri, 6 Dec 2019 at 03:14, Александр Дубровский
<dubrovvsskkyy using gmail.com> wrote:
>
> Task:
> A family of sets of letters is given. Find K for which one can construct a
> set consisting of K letters, each of them belonging to exactly K sets of a
> given family.
>
> Possible solution:
> For each letter, we will have a separate 'scoop', in which we will' put '
> the letter. This can be done using array A of 255 elements. In this case,
> the number of the 'scoop' corresponding to a letter is determined by the
> letter code (it is known that any letter is encoded by some binary number
> containing 8 digits - called bits; in Pascal, its code can be determined by
> using the ord function). When viewing the sets, let's count how many times
> each letter met. This is done as follows. When you meet a letter, increase
> the contents of the corresponding array element by 1. The initial contents
> of the array elements are 0. After viewing the letters of all sets,
> elements a determine the number of corresponding letters, and therefore the
> number of sets that have the corresponding letter (because in one set, all
> elements are different!). Using similarly array B from 255 elements (more
> need not, so as the desired the number of to on condition not exceeds
> number of letters) count the number of units, twos and so on in array A.
> Maximum significance index K, for which K=B[K] and will solution meet the
> tasks.
>
> [[alternative HTML version deleted]]
>
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