# print all permutations of string

Discussion in 'C Programming' started by anurag, Jul 20, 2006.

1. ### anuragGuest

hey can anyone help me in writing a code in c (function) that prints

anurag, Jul 20, 2006

2. ### Victor BazarovGuest

anurag wrote:
> hey can anyone help me in writing a code in c (function) that prints

Please, for C questions do not cross-post to comp.lang.c++. Thanks!

V
--
Please remove capital 'A's when replying by e-mail
I do not respond to top-posted replies, please don't ask

Victor Bazarov, Jul 20, 2006

3. ### Richard HeathfieldGuest

[comp.lang.c++ snipped - followups set to comp.lang.c]

anurag said:

> hey can anyone help me in writing a code in c (function) that prints

Consider how you would do this by hand. For example, let's look at the
string "ABCD". We can think of the permutations of this string as being
divided into four sets (because the string is four characters long):

1) All the strings starting with A and continuing with some permutation of
BCD
2) All the strings starting with B and continuing with some permutation of
CDA
3) All the strings starting with C and continuing with some permutation of
DAB
4) All the strings starting with D and continuing with some permutation of
ABC

As you might imagine, you can get at these sets simply by moving the string
around a little.

Let's look at just one of these sets (because the others are dealt with in
the same way, obviously): strings starting with A and continuing with some
permutation of BCD.

We are now faced with the problem of finding all the strings containing BCD
(which we can simply append to A to get the full permutation).

We can think of the permutations of this string as being divided into three
sets (because the string is three characters long):

1) All the strings starting with B and continuing with some permutation of
CD
2) All the strings starting with C and continuing with some permutation of
DB
3) All the strings starting with D and continuing with some permutation of
BC

As you might imagine, you can get at these sets simply by moving the string
around a little.

Let's look at just one of these sets (because the others are dealt with in
the same way, obviously): strings starting with (A and then) B and
continuing with some permutation of CD.

We are now faced with the problem of finding all the strings containing CD
(which we can simply append to AB to get the full permutation).

We can think of the permutations of this string as being divided into two
sets (because the string is two characters long):

1) All the strings starting with C and continuing with some permutation of D
2) All the strings starting with D and continuing with some permutation of C

As you might imagine, you can get at these sets simply by moving the string
around a little.

Let's look at just one of these sets (because the others are dealt with in
the same way, obviously): strings starting with (A and then B and then) C,
and continuing with some permutation of D.

We are now faced with the problem of finding all the strings containing D
(which we can simply append to ABC to get the full permutation).

We can think of the permutations of this string as being divided into one
set (because the string is one character long):

1) All the string starting with D - which is obvious, of course.

The canonical way to do this is via recursion, passing in the string,
together with the number of items yet to be permuted. If that number is 0,
simply display the string. Otherwise, loop around the leftmost
not-yet-handled character and, within the loop, recurse with n-1.

Now take a crack at it yourself, and let us know how you get on.

--
Richard Heathfield
"Usenet is a strange place" - dmr 29/7/1999
http://www.cpax.org.uk
email: rjh at above domain (but drop the www, obviously)

Richard Heathfield, Jul 20, 2006
4. ### Flash GordonGuest

anurag wrote:
> hey can anyone help me in writing a code in c (function) that prints

Yes. First learn that C++ and C are different languages, so posting to
comp.lang.c++ is entirely inappropriate if you want a C solution.

Having excluded comp.lang.c++ you should first try to write your
algorithm. comp.lang.c does not generally help with algorithms,
comp.programming and alt.comp.lang.c-c++ might, check the groups out to
see. comp.lang.c discusses the C language and helps people with C problems.

Then, post specific questions rather than just asking someone to help
you writing it. A lot of us could write the function in less time that
it would take to explain it to you, but this would not help you to learn.

If you don't know where to start, then I suggest you start off by trying
to write all the permutations of a short string by hand rather than
trying to write a program to do it. Then you can analyse how you did it
and try to formalise that in to an algorithm.

I've excluded comp.lang.c++ from the follow-ups. When you have decided
whether you have a problem with the C language or with writing the
algorithm please cut the posting down to only the most appropriate group.
--
Flash Gordon, living in interesting times.
Web site - http://home.flash-gordon.me.uk/
comp.lang.c posting guidelines and intro:
http://clc-wiki.net/wiki/Intro_to_clc

Flash Gordon, Jul 20, 2006
5. ### Lew PitcherGuest

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Hash: SHA1

anurag wrote:
> hey can anyone help me in writing a code in c (function) that prints

IIRC, this favour has been requested a number of times in recent weeks.
I wonder why the sudden interest in permuting strings using C
functions.

In any case, to give a concrete example of what R.H. discusses
elsethread, here's an attempt I made a few weeks ago, when the question
first came up. Take it as you will.

For the regulars: yes I know that answering a homework question is
frowned apon, and even worse is answering an algorithm question, but
this one piqued my interest. So, for my one freebie a year, I post this
code ;-)

==snip==

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

void rotate(unsigned length, char *string)
{
char save;

save = *string;
while(--length)
{
*string=*(string+1);
++string;
}
*string = save;
}

void permute(unsigned length, char *string, unsigned depth)
{

if (length == 0)
printf("%s\n",string-depth);
else
{
unsigned count;

for (count = length ; count > 0; --count)
{
permute(length-1,string+1,depth+1);
rotate(length,string);
}
}

}

int main(int argc, char **argv)
{
while (--argc)
{
char *source = malloc(strlen(*++argv)+1);

if (source)
{
strcpy(source,*argv);
printf("\nPermuting \"%s\"\n",source);

permute(strlen(source),source,0);

free(source);
}
}
return EXIT_SUCCESS;
}

==snip==

- --
Lew Pitcher

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Lew Pitcher, Jul 20, 2006
6. ### IcoGuest

In comp.lang.c Richard Heathfield <> wrote:
> [comp.lang.c++ snipped - followups set to comp.lang.c]
>
> anurag said:
>
>> hey can anyone help me in writing a code in c (function) that prints

>
> Consider how you would do this by hand. For example, let's look at the
> string "ABCD". We can think of the permutations ...

[ ...snipped yet another lengthy explanation... ]

> ... string. Otherwise, loop around the leftmost
> not-yet-handled character and, within the loop, recurse with n-1.
>
> Now take a crack at it yourself, and let us know how you get on.

I admire your patience, I really do...

--
:wq
^X^Cy^K^X^C^C^C^C

Ico, Jul 20, 2006
7. ### Francis GlassborowGuest

In article <>,
anurag <> writes
>hey can anyone help me in writing a code in c (function) that prints
>

That looks like homework. In addition it is under specified. Are the
characters in the string all unique or are repeats allowed? If they are
all unique it is very easy

--
Francis Glassborow ACCU
Author of 'You Can Do It!' and "You Can Program in C++"
see http://www.spellen.org/youcandoit
For project ideas and contributions: http://www.spellen.org/youcandoit/projects

Francis Glassborow, Jul 20, 2006
8. ### Keith ThompsonGuest

Francis Glassborow <> writes:
> In article <>,
> anurag <> writes
>>hey can anyone help me in writing a code in c (function) that prints
>>

>
> That looks like homework. In addition it is under specified. Are the
> characters in the string all unique or are repeats allowed? If they
> are all unique it is very easy

Not as easy as if they're all the same!

--
Keith Thompson (The_Other_Keith) <http://www.ghoti.net/~kst>
San Diego Supercomputer Center <*> <http://users.sdsc.edu/~kst>
We must do something. This is something. Therefore, we must do this.

Keith Thompson, Jul 20, 2006
9. ### Noah RobertsGuest

anurag wrote:
> hey can anyone help me in writing a code in c (function) that prints

Knuth, Volume 4 fascicle 2.

Noah Roberts, Jul 20, 2006
10. ### Alf P. SteinbachGuest

* Noah Roberts:
> anurag wrote:
>> hey can anyone help me in writing a code in c (function) that prints

>
> Knuth, Volume 4 fascicle 2.

As I recall, Knuth does not discuss or mention arithmetic coding of
permutations (using the factorial number system), so is not a complete
reference.

--
A: Because it messes up the order in which people normally read text.
Q: Why is it such a bad thing?
A: Top-posting.
Q: What is the most annoying thing on usenet and in e-mail?

Alf P. Steinbach, Jul 20, 2006
11. ### Ben PfaffGuest

"Alf P. Steinbach" <> writes:

> * Noah Roberts:
>> anurag wrote:
>>> hey can anyone help me in writing a code in c (function) that prints

>> Knuth, Volume 4 fascicle 2.

>
> As I recall, Knuth does not discuss or mention arithmetic coding of
> permutations (using the factorial number system), so is not a complete
> reference.

Is that necessary to answer the OP's question? I doubt it.
--
"doe not call up Any that you can not put downe."
--H. P. Lovecraft

Ben Pfaff, Jul 20, 2006
12. ### Kenneth BrodyGuest

Lew Pitcher wrote:
>
> -----BEGIN PGP SIGNED MESSAGE-----
> Hash: SHA1
>
> anurag wrote:
> > hey can anyone help me in writing a code in c (function) that prints

>
> IIRC, this favour has been requested a number of times in recent weeks.
> I wonder why the sudden interest in permuting strings using C
> functions.

Perhaps from summer school assignments from all those students who
failed their C classes?

[...]

--
+-------------------------+--------------------+-----------------------+
| Kenneth J. Brody | www.hvcomputer.com | #include |
| kenbrody/at\spamcop.net | www.fptech.com | <std_disclaimer.h> |
+-------------------------+--------------------+-----------------------+
Don't e-mail me at: <mailto:>

Kenneth Brody, Jul 21, 2006
13. ### Noah RobertsGuest

Alf P. Steinbach wrote:
> * Noah Roberts:
> > anurag wrote:
> >> hey can anyone help me in writing a code in c (function) that prints

> >
> > Knuth, Volume 4 fascicle 2.

>
> As I recall, Knuth does not discuss or mention arithmetic coding of
> permutations (using the factorial number system), so is not a complete
> reference.

Yeah, I don't know what's actually in it. I have it but haven't gotten
the time to read it yet. Knuth takes me an extraordinary amount of
time to read. But it's title is "Generating all permutations and
combinations" so I figured it would be appropriate. Guy might learn
something instead of having his homework done for him.

Noah Roberts, Jul 21, 2006
14. ### Simon BiberGuest

Alf P. Steinbach wrote:
> * Noah Roberts:
>> anurag wrote:
>>> hey can anyone help me in writing a code in c (function) that prints

>>
>> Knuth, Volume 4 fascicle 2.

>
> As I recall, Knuth does not discuss or mention arithmetic coding of
> permutations (using the factorial number system), so is not a complete
> reference.

When you refer to arithmetic coding of permutations using the factorial
number system, are you talking about an algorithm that assigns a unique
index number to each permutation and can return any individual
permutation given its index number?

I have implemented a system like that below:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

typedef unsigned long long ull;

/* calculate factorial of given number */
ull fact(ull a)
{
ull result = 1;
while(a) result *= a--;
return result;
}

/* generates a permutation of str and stores it in 'rs'
the permutation generated is index number 'no'
of 'np' total permutations (np == fact(strlen(str)) */
void get_perm(char *rs, const char *str, ull no, ull np)
{
size_t len = strlen(str);
ull nm = no;
ull lt;
char *p;
char temp;
strcpy(rs, str);

for(p = rs; *p; p++)
{
np = np / len;
lt = nm / np;
nm = nm % np;

temp = p[0];
p[0] = p[lt];
p[lt] = temp;

len--;
}
}

void print_all(const char *str)
{
size_t len = strlen(str);
char *rs = malloc(len + 1);
ull np = fact(len);
ull i;
if(!rs)
{
fprintf(stderr, "Error allocating memory\n");
}
else for(i = 0; i < np; i++)
{
get_perm(rs, str, i, np);
printf("%4lld: %s\n", i, rs);
}
}

int main(int argc, char **argv)
{
if(argc == 2)
{
print_all(argv[1]);
}
else
{
fprintf(stderr, "Error: require one argument for"
" string to permute\n");
}
return 0;
}

Simon Biber, Jul 21, 2006
15. ### lovecreatesbeautyGuest

Lew Pitcher wrote:
> For the regulars: yes I know that answering a homework question is
> frowned apon, and even worse is answering an algorithm question, but
> this one piqued my interest. So, for my one freebie a year, I post this
> code ;-)

The code gives the same amount of permutations for following two cases,
is it correct?

Permuting "abcde"
abcde
abced
....

Permuting "abcdd"
abcdd
abcdd
....

lovecreatesbeauty, Jul 25, 2006
16. ### lovecreatesbeautyGuest

Richard Heathfield wrote:
> [comp.lang.c++ snipped - followups set to comp.lang.c]
>
> anurag said:
>
> > hey can anyone help me in writing a code in c (function) that prints

>
> Consider how you would do this by hand. For example, let's look at the
> string "ABCD". We can think of the permutations of this string as being
> divided into four sets (because the string is four characters long):

<snip>

If you can demonstrate your explanation with real quality code, it will
be better, and it shows you achieve what you can say.

lovecreatesbeauty, Jul 25, 2006
17. ### lovecreatesbeautyGuest

Ben Pfaff wrote:
> "Alf P. Steinbach" <> writes:
>
> > * Noah Roberts:
> >> anurag wrote:
> >>> hey can anyone help me in writing a code in c (function) that prints
> >> Knuth, Volume 4 fascicle 2.

> >
> > As I recall, Knuth does not discuss or mention arithmetic coding of
> > permutations (using the factorial number system), so is not a complete
> > reference.

>
> Is that necessary to answer the OP's question? I doubt it.
> --
> "doe not call up Any that you can not put downe."
> --H. P. Lovecraft

Why? Up to now, the code given by you C experts are all wrong. Are you
all line-shooters?

lovecreatesbeauty, Jul 25, 2006
18. ### Ben PfaffGuest

"lovecreatesbeauty" <> writes:

> Why? Up to now, the code given by you C experts are all wrong. Are you
> all line-shooters?

Some code I wrote for generating permutations can be found in
ll_next_permutation and ll_prev_permutation at
http://cvs.savannah.gnu.org/viewcvs/pspp/src/libpspp/ll.c?rev=1.1&root=pspp&view=markup
It targets linked lists, not strings.

There's a test program at
http://cvs.savannah.gnu.org/viewcvs...t.c?content-type=text/plain&rev=1.1&root=pspp
--
int main(void){char p[]="ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz.\
\n",*q="kl BIcNBFr.NKEzjwCIxNJC";int i=sizeof p/2;char *strchr();int putchar(\
);while(*q){i+=strchr(p,*q++)-p;if(i>=(int)sizeof p)i-=sizeof p-1;putchar(p\
);}return 0;}

Ben Pfaff, Jul 25, 2006
19. ### Richard HeathfieldGuest

lovecreatesbeauty said:

> Richard Heathfield wrote:
>> [comp.lang.c++ snipped - followups set to comp.lang.c]
>>
>> anurag said:
>>
>> > hey can anyone help me in writing a code in c (function) that prints

>>
>> Consider how you would do this by hand. For example, let's look at the
>> string "ABCD". We can think of the permutations of this string as being
>> divided into four sets (because the string is four characters long):

> <snip>
>
> If you can demonstrate your explanation with real quality code, it will
> be better, and it shows you achieve what you can say.

That's great psychology, but doing his homework for him is not going to help
him one bit. If you choose to believe that I can't permute a string, that's
entirely up to you. I am not here to impress you.

--
Richard Heathfield
"Usenet is a strange place" - dmr 29/7/1999
http://www.cpax.org.uk
email: rjh at above domain (but drop the www, obviously)

Richard Heathfield, Jul 25, 2006
20. ### Ivanna PeeGuest

Lew Pitcher wrote:
> -----BEGIN PGP SIGNED MESSAGE-----
> Hash: SHA1
>
>
> anurag wrote:
> > hey can anyone help me in writing a code in c (function) that prints

>
> IIRC, this favour has been requested a number of times in recent weeks.
> I wonder why the sudden interest in permuting strings using C
> functions.
>
> In any case, to give a concrete example of what R.H. discusses
> elsethread, here's an attempt I made a few weeks ago, when the question
> first came up. Take it as you will.
>
> For the regulars: yes I know that answering a homework question is
> frowned apon, and even worse is answering an algorithm question, but
> this one piqued my interest. So, for my one freebie a year, I post this
> code ;-)
>
> ==snip==
>
> #include <stdio.h>
> #include <stdlib.h>
> #include <string.h>
>
> void rotate(unsigned length, char *string)
> {
> char save;
>
> save = *string;
> while(--length)
> {
> *string=*(string+1);
> ++string;
> }
> *string = save;
> }
>
> void permute(unsigned length, char *string, unsigned depth)
> {
>
> if (length == 0)
> printf("%s\n",string-depth);
> else
> {
> unsigned count;
>
> for (count = length ; count > 0; --count)
> {
> permute(length-1,string+1,depth+1);
> rotate(length,string);
> }
> }
>
> }
>
>
> int main(int argc, char **argv)
> {
> while (--argc)
> {
> char *source = malloc(strlen(*++argv)+1);
>
> if (source)
> {
> strcpy(source,*argv);
> printf("\nPermuting \"%s\"\n",source);
>
> permute(strlen(source),source,0);
>
> free(source);
> }
> }
> return EXIT_SUCCESS;
> }
>
>
> ==snip==
>
> - --
> Lew Pitcher
>
>
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>
> iD8DBQFEv84lagVFX4UWr64RAq3YAKDBs4//FGSrc+zn7+duG2bRtCuRaQCfSnOS
> mg6QbOGNExUVVsXBp5lQYD8=
> =pYBy
> -----END PGP SIGNATURE-----

Now try it recursively.

Ivanna Pee, Jul 25, 2006