# Spiral Access of 2 d array.

Discussion in 'C Programming' started by mail2sandeepnl@gmail.com, Aug 29, 2007.

1. ### Guest

Hi
how to spirally access 2 d array,

ex:
for input array
1 2 3 4
5 6 7 8
9 10 11 12

output should be like : 1,2,3,4,8,12,11,10,9,5,6,7
i thought of some iterative method, but not satisfied, is there any
recursive solution for this kind of problem ?

, Aug 29, 2007

2. ### Ivan GotovchitsGuest

wrote:

> Hi
> how to spirally access 2 d array,
>
> ex:
> for input array
> 1 2 3 4
> 5 6 7 8
> 9 10 11 12
>
> output should be like : 1,2,3,4,8,12,11,10,9,5,6,7
> i thought of some iterative method, but not satisfied, is there any
> recursive solution for this kind of problem ?

Not sure, and not tested, but try something like this:

void get_frame(int **array, int *output, int rows, int cols);

int
main(void)
{
int array[X][Y];
int result[X+Y];
int x = X, y = Y;

while(x && y) {
get_frame(array, result, x, y);
result += (2*x + 2*y);
x--;
y--;
}
}

void
get_frame(int **array, int *output, int rows, int cols)
{
int i,j,k = 0;

for(j = 0; j < cols; j++) {
output[k++] = array[0][j];
}
for(i = 0; i < rows; i++) {
output[k++] = array[cols];
}
for(j = cols; j > 0; j--) {
output[k++] = array[rows][j];
}
for(i = rows; i > 1; i--) {
output[k++] = array[0];
}
}

Yes, it is rather crude ))

Ivan Gotovchits, Aug 29, 2007

3. ### Ivan GotovchitsGuest

Ivan Gotovchits wrote:

> wrote:

<snip>
> Yes, it is rather crude ))

This varian is more correct ...
#define X = 10
#define Y = 10
void get_frame(int **array, int *output, int rows, int cols);

int
main(void)
{
int array[X][Y];
int result[X+Y];
int x = X, y = Y;
int i = 0, j = 0;

while(x && y) {
array = &array[i++][j++];
get_frame(array, result, x, y);
result += (2*x + 2*y);
x--;
y--;
}
}

void
get_frame(int **array, int *output, int rows, int cols)
{
int i,j,k = 0;

for(j = 0; j < cols; j++) {
output[k++] = array[0][j];
}
for(i = 0; i < rows; i++) {
output[k++] = array[cols];
}
for(j = cols; j > 0; j--) {
output[k++] = array[rows][j];
}
for(i = rows; i > 1; i--) {
output[k++] = array[0];
}
}

Ivan Gotovchits, Aug 29, 2007
4. ### Richard HeathfieldGuest

Ivan Gotovchits said:

> Ivan Gotovchits wrote:
>
>> wrote:

> <snip>
>> Yes, it is rather crude ))

> This varian is more correct ...

Yet it is not correct. The compiler must issue a diagnostic message for
the code you supplied. For example, my own compiler of choice issues
the following output when presented with your code:

foo.c: In function `main':
foo.c:8: parse error before `='
foo.c:9: parse error before `='
foo.c:10: parse error before `='
foo.c:13: `y' undeclared (first use in this function)
foo.c:13: (Each undeclared identifier is reported only once
foo.c:13: for each function it appears in.)
foo.c:14: `array' undeclared (first use in this function)
foo.c:15: `result' undeclared (first use in this function)
foo.c:20: warning: control reaches end of non-void function
make: *** [foo.o] Error 1

<snip>

--
Richard Heathfield <http://www.cpax.org.uk>
Email: -www. +rjh@
"Usenet is a strange place" - dmr 29 July 1999

Richard Heathfield, Aug 29, 2007
5. ### Joachim SchmitzGuest

"Ivan Gotovchits" <> schrieb im Newsbeitrag
news:fb3ls7\$b4c\$...
> Ivan Gotovchits wrote:
>
>> wrote:

> <snip>
>> Yes, it is rather crude ))

> This varian is more correct ...
> #define X = 10
> #define Y = 10

#define X 10
#define Y 10

> void get_frame(int **array, int *output, int rows, int cols);
>
> int
> main(void)
> {
> int array[X][Y];
> int result[X+Y];
> int x = X, y = Y;
> int i = 0, j = 0;
>
> while(x && y) {
> array = &array[i++][j++];
> get_frame(array, result, x, y);
> result += (2*x + 2*y);
> x--;
> y--;
> }

return 0;

> }
>
> void
> get_frame(int **array, int *output, int rows, int cols)
> {
> int i,j,k = 0;
>
> for(j = 0; j < cols; j++) {
> output[k++] = array[0][j];
> }
> for(i = 0; i < rows; i++) {
> output[k++] = array[cols];
> }
> for(j = cols; j > 0; j--) {
> output[k++] = array[rows][j];
> }
> for(i = rows; i > 1; i--) {
> output[k++] = array[0];
> }
> }
>

Bye, Jojo

Joachim Schmitz, Aug 29, 2007
6. ### raviGuest

On Aug 29, 3:11 pm, ""
<> wrote:
> Hi
> how to spirally access 2 d array,
>
> ex:
> for input array
> 1 2 3 4
> 5 6 7 8
> 9 10 11 12
>
> output should be like : 1,2,3,4,8,12,11,10,9,5,6,7
> i thought of some iterative method, but not satisfied, is there any
> recursive solution for this kind of problem ?

int Spiral(int n,int x,int y,int i)
{
while(1)
-----{
----------if(x==0)
----------{
---------------return (i+y);
----------}
----------else if(y==n-1)
----------{
---------------return (i+n+x);
----------}
----------else if(x==n-1)
----------{
---------------return (i+ 3(n-1)-y);
----------}
----------else if(y==n-1)
----------{
---------------return(i+ 4(n-1) -x);
----------}
----------else
----------{
--------------- x=x-1;
--------------- y=y-1;
--------------- i=i+ 4(n-1);
--------------- n=n-2;
----------}
-----}
}

//Now Call the function for each x,y;

int s=1;

//The No. from which you want your spiral to begin;
eg. for s=5,n=3 the spiral will be

5 6 7
12 13 8
11 10 9

for(int i=0;i<n;i++)
{
-----for(int j=0;j<n;j++)
-----{
----------cout<<Spiral(n,i,j,s)<<" ";
-----}
-----cout<<"\n";
}

ravi, Aug 29, 2007
7. ### Ben BacarisseGuest

"" <> writes:

> Hi
> how to spirally access 2 d array,
>
> ex:
> for input array
> 1 2 3 4
> 5 6 7 8
> 9 10 11 12
>
> output should be like : 1,2,3,4,8,12,11,10,9,5,6,7
> i thought of some iterative method, but not satisfied, is there any
> recursive solution for this kind of problem ?

In C, recursive functions on 2D arrays are not common. Since C can't
slice an array in anything but very simple ways, recursion is less
useful than with other parameter types. I can image (but these days
could not code!) nice recursive solutions in Algol 68.

This may be homework, but the following unlikely to score many marks
but it probably is how I'd do it. With all the right comments, it is

#include <stdio.h>

#define N 5
#define M 3

int min(int a, int b)
{
return a < b ? a : b;
}

void spiral(int mat[M][N])
{
int n = N, d = +1, i = 0, j = -1;
int s, segl = N + M - 1;
for (s = 0; s < min(N, M); s++, d = -d, segl -= 2, n--) {
int c, *ip = &j;
for (c = 0; c < segl; c++) {
if (c == n)
ip = &i;
*ip += d;
printf("%3d", mat[j]);
}
}
}

int main(void)
{
int matrix[M][N];
int i, j;
for (i = 0; i < M; i++)
for (j = 0; j < N; j++)
matrix[j] = i * N + j + 1;

for (i = 0; i < M; i++) {
for (j = 0; j < N; j++)
printf("%3d", matrix[j]);
printf("\n");
}

spiral(matrix);
printf("\n");
return 0;
}

--
Ben.

Ben Bacarisse, Aug 29, 2007
8. ### Keith ThompsonGuest

Ivan Gotovchits <> writes:
> Ivan Gotovchits wrote:
>
>> wrote:

> <snip>
>> Yes, it is rather crude ))

> This varian is more correct ...
> #define X = 10
> #define Y = 10

Dropping the '=' characters will fix *some* of your problems.

> void get_frame(int **array, int *output, int rows, int cols);
>
> int
> main(void)
> {
> int array[X][Y];
> int result[X+Y];
> int x = X, y = Y;
> int i = 0, j = 0;
>
> while(x && y) {
> array = &array[i++][j++];

You can't assign to an array.

> get_frame(array, result, x, y);

The first parameter to get_frame() is of type int**. You're passing
it an argument of type int (*)[10].

> result += (2*x + 2*y);

Again, you can't assign to an array.

[snip]

Please don't post code, particularly a sizable program like this,
unless you've compiled it yourself.

If your errors were the result of fundamental misunderstandings, I
suggest reading section 6 of the comp.lang.c FAQ,
<http://www.c-faq.com/>.

--
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."
-- Antony Jay and Jonathan Lynn, "Yes Minister"

Keith Thompson, Aug 29, 2007
9. ### Keith ThompsonGuest

ravi <> writes:
[snip]
> for(int i=0;i<n;i++)
> {
> -----for(int j=0;j<n;j++)
> -----{
> ----------cout<<Spiral(n,i,j,s)<<" ";
> -----}
> -----cout<<"\n";
> }

What is the purpose of the rows of hyphens on each line, other than to
make the code impossible to compile?

Dropping the '-'s, this code is C++, not C.

--
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."
-- Antony Jay and Jonathan Lynn, "Yes Minister"

Keith Thompson, Aug 29, 2007