Rotate array clockwise

Question

Lets start out with an simple 16 x 16 array of ints.
How would I insert the 'SomeValue' into the array in a 90 degree clockwise order.

int[] image = new int[16 * 16];

for (int x = 0; x < 16; x++)
{
    for (int y = 0; y < 16; y++)
    {
        int someValue = x * y;

        // This is the line I think is wrong
        image[x + (y * 16)] = someValue; 
    }
}

The result should be like the Rotated Array below.

Normal order:
0, 1, 2,
3, 4, 5,
6, 7, 8,

Rotated Clockwise:
6, 3, 0,
7, 4, 1,
8, 5, 2,

Your code does not compile, z is not declared. You should also simplify your life by using a 2 dimensional array like int[,] image = new int[16, 16]; — Albin Sunnanbo
– Albin Sunnanbo, Commented Nov 4, 2010 at 21:51
What's z? Do you want to rotate the matrix or insert values into it? Those are two different things. — Pedro Silva
– Pedro Silva, Commented Nov 4, 2010 at 21:51
now it compiles, what do you expect the code to do? Generate the "Rotated Clockwise" array? — Albin Sunnanbo
– Albin Sunnanbo, Commented Nov 4, 2010 at 21:56
I want to insert the 'SomeValue' in the image array in a way the image becomes rotated 90 degrees Clockwise. — Jeremi Stadler
– Jeremi Stadler, Commented Nov 4, 2010 at 22:00

dtb · Accepted Answer · 2010-11-04 22:11:55Z

6

Are you looking for something like this?

0 0 0 1 1 1 2 2 2   x
0 1 2 0 1 2 0 1 2   y
= = = = = = = = =
6 3 0 7 4 1 8 5 2   m*(m-1-y)+x

for m=3.

const int m = 16;
int[] image = new int[m * m];

for (int x = 0; x < m; x++)
{
    for (int y = 0; y < m; y++)
    {
        int someValue = x * y;

        image[m*(m-1-y)+x] = someValue; 
    }
}

edited Nov 4, 2010 at 22:11

answered Nov 4, 2010 at 22:04

dtb

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2 Comments

lvictorino Over a year ago

And what about rectangle arrays? what if instead of [16*16] we need to rotate a [5*2] array ?

Marcin Over a year ago

For rectangles:

int[] copy = new int[source.Length]; int i = 0; for(int x=0; x < width; x++) { for(int y=height-1; y >= 0; y--) {copy[i++] = source[y * width + x];}}

. Note that you now assume width becomes height and vice versa in the "copy" array

Community · Accepted Answer · 2017-05-23 12:24:20Z

2

Follow @Albin Sunnanbos suggestion and use a two-dimensional array. Then have a look at this related question.

edited May 23, 2017 at 12:24

CommunityBot

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answered Nov 4, 2010 at 21:59

Anders Fjeldstad

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2 Comments

Jeremi Stadler Over a year ago

Do you know how to rotate it in a counter clockwise way??

Dialecticus Over a year ago

My sense of symmetry tells me to use [3-j,i] instead of [j,3-i]. In your case it's 15 instead of 3.

Albin Sunnanbo · Accepted Answer · 2010-11-04 22:04:39Z

1

If you want to generate the rotated array you can do like this

int[,] image = new int[16 , 16];

int current = 0;
for (int x = 15; x >= 0; x--)
{
    for (int y = 0; y < 16; y++)
    {
        image[x, y] = current;
        current++;
    }
}

// Output

for (int y = 0; y < 16; y++)
{
    for (int x = 0; x < 16; x++)
    {
        Console.Write(image[x,y] + ", ");
    }
    Console.WriteLine();
}

answered Nov 4, 2010 at 22:04

Albin Sunnanbo

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3 Comments

Jeremi Stadler Over a year ago

Well it outputs in a two dimensional array but I can convert that easily :D

Albin Sunnanbo Over a year ago

The two dimensional array is not a bug, it is a feature :-) (it improves the readability and intent of the code)

Jeremi Stadler Over a year ago

You're right! The two dimensional array actual makes it easier :D

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