I have a set of X items, but want permutations of length Y (X > Y). I
am aware of the permutation functions in <algorithm>, but I don't
believe this will do what I want. Is there a way, either through the
STL or some other library to do this, or do I need to write my own
code? 20  1470 
John Trunek wrote: I have a set of X items, but want permutations of length Y (X > Y). I
am aware of the permutation functions in <algorithm>, but I don't
believe this will do what I want. Is there a way, either through the
STL or some other library to do this, or do I need to write my own
code?
Your terminology is non-standard (and I'm not talking about the C++
standard). A permutation of a set S is a bijective map from S to S.
My guess is that you want the set of images of permutations of Y-
subsets of S (where S is your set of X items, and where a 'Y-subset'
of S is a subset of S which has Y elements).
You need to write your own function for this. It will be easiest
to make the function recursive, at least to begin with, I think.
Post your attempt here and I'm sure you will get help.
--
Regards,
Buster.
John Trunek wrote: I have a set of X items, but want permutations of length Y (X > Y). I
am aware of the permutation functions in <algorithm>, but I don't
believe this will do what I want. Is there a way, either through the
STL or some other library to do this, or do I need to write my own
code?
Your terminology is non-standard (and I'm not talking about the C++
standard). A permutation of a set S is a bijective map from S to S.
My guess is that you want the set of images of permutations of Y-
subsets of S (where S is your set of X items, and where a 'Y-subset'
of S is a subset of S which has Y elements).
You need to write your own function for this. It will be easiest
to make the function recursive, at least to begin with, I think.
Post your attempt here and I'm sure you will get help.
--
Regards,
Buster.
Buster wrote: John Trunek wrote:
I have a set of X items, but want permutations of length Y (X > Y). I
am aware of the permutation functions in <algorithm>, but I don't
believe this will do what I want. Is there a way, either through the
STL or some other library to do this, or do I need to write my own
code?
Your terminology is non-standard (and I'm not talking about the C++
standard). A permutation of a set S is a bijective map from S to S.
My guess is that you want the set of images of permutations of Y-
subsets of S (where S is your set of X items, and where a 'Y-subset'
of S is a subset of S which has Y elements).
s/images of permutations/permutations of images/
You need to write your own function for this. It will be easiest
to make the function recursive, at least to begin with, I think.
Post your attempt here and I'm sure you will get help.
--
Regards,
Buster.
Buster wrote: John Trunek wrote:
I have a set of X items, but want permutations of length Y (X > Y). I
am aware of the permutation functions in <algorithm>, but I don't
believe this will do what I want. Is there a way, either through the
STL or some other library to do this, or do I need to write my own
code?
Your terminology is non-standard (and I'm not talking about the C++
standard). A permutation of a set S is a bijective map from S to S.
My guess is that you want the set of images of permutations of Y-
subsets of S (where S is your set of X items, and where a 'Y-subset'
of S is a subset of S which has Y elements).
s/images of permutations/permutations of images/
You need to write your own function for this. It will be easiest
to make the function recursive, at least to begin with, I think.
Post your attempt here and I'm sure you will get help.
--
Regards,
Buster.
Buster wrote: Buster wrote:
John Trunek wrote:
I have a set of X items, but want permutations of length Y (X > Y). I
am aware of the permutation functions in <algorithm>, but I don't
believe this will do what I want. Is there a way, either through the
STL or some other library to do this, or do I need to write my own
code?
Your terminology is non-standard (and I'm not talking about the C++
standard). A permutation of a set S is a bijective map from S to S.
My guess is that you want the set of images of permutations of Y-
subsets of S (where S is your set of X items, and where a 'Y-subset'
of S is a subset of S which has Y elements).
s/images of permutations/permutations of images/
No, sorry, let it stand. I meant the images of the permutations,
viewing the permutations as functions, as I said. To be clear, these
sets, the images of the permutations of a set T (say), are what might
be called the 'results of permuting T', or just 'the permutations of T',
speaking less formally.
Another obscurity is the meaning of the word 'set' in this context.
The OP may have been referring to the standard library's 'set' class
template, as well as alluding to the set-theoretic term 'set'. You need to write your own function for this. It will be easiest
to make the function recursive, at least to begin with, I think.
Post your attempt here and I'm sure you will get help.
--
Regards,
Buster.
Buster wrote: Buster wrote:
John Trunek wrote:
I have a set of X items, but want permutations of length Y (X > Y). I
am aware of the permutation functions in <algorithm>, but I don't
believe this will do what I want. Is there a way, either through the
STL or some other library to do this, or do I need to write my own
code?
Your terminology is non-standard (and I'm not talking about the C++
standard). A permutation of a set S is a bijective map from S to S.
My guess is that you want the set of images of permutations of Y-
subsets of S (where S is your set of X items, and where a 'Y-subset'
of S is a subset of S which has Y elements).
s/images of permutations/permutations of images/
No, sorry, let it stand. I meant the images of the permutations,
viewing the permutations as functions, as I said. To be clear, these
sets, the images of the permutations of a set T (say), are what might
be called the 'results of permuting T', or just 'the permutations of T',
speaking less formally.
Another obscurity is the meaning of the word 'set' in this context.
The OP may have been referring to the standard library's 'set' class
template, as well as alluding to the set-theoretic term 'set'. You need to write your own function for this. It will be easiest
to make the function recursive, at least to begin with, I think.
Post your attempt here and I'm sure you will get help.
--
Regards,
Buster.
* Buster <no***@nowhere. com> schriebt: John Trunek wrote: I have a set of X items, but want permutations of length Y (X > Y). I
am aware of the permutation functions in <algorithm>, but I don't
believe this will do what I want. Is there a way, either through the
STL or some other library to do this, or do I need to write my own
code?
Your terminology is non-standard (and I'm not talking about the C++
standard). A permutation of a set S is a bijective map from S to S.
My guess is that you want the set of images of permutations of Y-
subsets of S (where S is your set of X items, and where a 'Y-subset'
of S is a subset of S which has Y elements).
I think it's more reasonable to assume that the OP wants to generate all
possible passwords of length Y from some character set with X characters.
In which case it's combinations, not permutations. I think.
You need to write your own function for this. It will be easiest
to make the function recursive, at least to begin with, I think.
Post your attempt here and I'm sure you will get help.
If assumption above is correct then the easiest is probably to just
count up; but the easiest programmaticall y will not be very efficient
in light of some combinations being far more probable than others.
--
A: Because it messes up the order in which people normally read text.
Q: Why is top-posting such a bad thing?
A: Top-posting.
Q: What is the most annoying thing on usenet and in e-mail?
* Buster <no***@nowhere. com> schriebt: John Trunek wrote: I have a set of X items, but want permutations of length Y (X > Y). I
am aware of the permutation functions in <algorithm>, but I don't
believe this will do what I want. Is there a way, either through the
STL or some other library to do this, or do I need to write my own
code?
Your terminology is non-standard (and I'm not talking about the C++
standard). A permutation of a set S is a bijective map from S to S.
My guess is that you want the set of images of permutations of Y-
subsets of S (where S is your set of X items, and where a 'Y-subset'
of S is a subset of S which has Y elements).
I think it's more reasonable to assume that the OP wants to generate all
possible passwords of length Y from some character set with X characters.
In which case it's combinations, not permutations. I think.
You need to write your own function for this. It will be easiest
to make the function recursive, at least to begin with, I think.
Post your attempt here and I'm sure you will get help.
If assumption above is correct then the easiest is probably to just
count up; but the easiest programmaticall y will not be very efficient
in light of some combinations being far more probable than others.
--
A: Because it messes up the order in which people normally read text.
Q: Why is top-posting such a bad thing?
A: Top-posting.
Q: What is the most annoying thing on usenet and in e-mail?
Alf P. Steinbach wrote: * Buster <no***@nowhere. com> schriebt:
John Trunek wrote:
I have a set of X items, but want permutations of length Y (X > Y). I
am aware of the permutation functions in <algorithm>, but I don't
believe this will do what I want. Is there a way, either through the
STL or some other library to do this, or do I need to write my own
code?
Your terminology is non-standard (and I'm not talking about the C++
standard). A permutation of a set S is a bijective map from S to S.
My guess is that you want the set of images of permutations of Y-
subsets of S (where S is your set of X items, and where a 'Y-subset'
of S is a subset of S which has Y elements).
I think it's more reasonable to assume that the OP wants to generate all
possible passwords of length Y from some character set with X characters.
In which case it's combinations, not permutations. I think.
The original post doesn't suggest that to me. Looks like we'll need a
clarification. (I don't quite follow your suggestion either. Is "xyz"
the same password as "zyx"?) You need to write your own function for this. It will be easiest
to make the function recursive, at least to begin with, I think.
Post your attempt here and I'm sure you will get help.
If assumption above is correct then the easiest is probably to just
count up; but the easiest programmaticall y will not be very efficient
in light of some combinations being far more probable than others.
All passwords of length Y from a character set with X characters are
equally 'probable' (think 'lottery'). In the obvious thought experiment,
each distinct password has probability 'std::pow (X, -Y);'.
--
Regards,
Buster. This thread has been closed and replies have been disabled. Please start a new discussion. Similar topics | |
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last post by:
Hi,
I am trying to come up with a way to develop all n-length permutations of a
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Thanks for your help,
|
by: John Trunek |
last post by:
I have a set of X items, but want permutations of length Y (X > Y). I
am aware of the permutation functions in <algorithm>, but I don't
believe this will do what I want. Is there a way, either through the
STL or some other library to do this, or do I need to write my own
code?
|
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last post by:
Does STL contain algorithms which generate (enable to generate) exponents, permutations, arrangements, and combinations for any
numbers and words?
--
Alex Vinokur
mailto:alexvn@connect.to
http://mathforum.org/library/view/10978.html
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"""
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