Matrix Rotation 90 degrees (keep it up)

An image is represented as a nxn matrix. each pixel in the image is 4 bytes. Write a function to rotate the image 90 degrees. Can you perform operations in the same place? (That is, do not open up additional storage space)

The first question is the element of an exchange matrix:

For example, 3*3 Matrices

1 2 3
4 5 6
7 8 9
First, process the first line and rotate four elements counterclockwise at a time. The following is a second operation.
3 2 9 3 6 9
4 5 6 2 5 8
1 8 7 1 4 7
The first second time

For a matrix of 5*5
1 2 3 4 5
6 7 8 9 10
11 12 13 14 15
16 17 18 19 20
21 22 23 24 25
Here is the change after the first line.
5 2 3 4 25
6 7 8 9 10
11 12 13 14 15
16 17 18 19 20
1 22 23 24 21
1st times

5 10 3 4 25
6 7 8 9 24
11 12 13 14 15
2 17 18 19 20
1 22 23 16 21
2nd times

5 10 15 4 25
6 7 8 9 24
3 12 13 14 23
2 17 18 19 20
1 22 11 16 21
3rd Times

5 10 15 20 25
4 7 8 9 24
3 12 13 14 23
2 17 18 19 22
1 6 11 16 21
4th times

After the first line is processed
What is not processed is a 3*3 matrix.
7 8 9
12 12 13
17 18 19
The result is obtained after processing in 3*3.
5 10 15 20 25
4 9 14 19 24
3 8 13 18 23
2 7 12 17 22
1 6 11 16 21
However, when writing code, this encoding method is troublesome. It is very troublesome to handle array subscript calculation.

The following describes another method.
Let's look at the 4*4 matrix.
1 2 3 4
5 6 7 8
9 10 11 12
13 14 15 16
We wire the elements on both sides of the main diagonal line:
1 5 9 13
2 6 10 14
3 7 11 15
4 8 12 16
Then the result is obtained by swapping the elements of row I and row n-i-1.
4 8 12 16
3 7 11 15
2 6 10 14
1 5 9 13

The following code is used:

# Define N 4 void swap (Int & vleft, Int & vright) {int temp = vleft; vleft = vright; vright = temp ;} // rotate void rotate_matrix (INT vmat [N] [N]) counterclockwise {// first swap the elements on both sides of the main diagonal line. If it is clockwise, for (INT I = 0; I <n ;++ I) {for (int K = I + 1; k <n ;++ K) {swap (vmat [I] [K], vmat [k] [I]) ;}// element for (INT I = 0; I <n/2; ++ I) {for (int K = 0; k <n; ++ K) {swap (vmat [I] [K], vmat [N-i-1] [k]) ;}} void print_matrix (INT vmat [N] [N]) {for (INT I = 0; I <n; ++ I) {for (int K = 0; k <n; ++ K) {printf ("% 3d", vmat [I] [k]);} printf ("\ n") ;}} int main () {int a [n] [N] = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16}; print_matrix (a); printf ("\ n"); rotate_matrix (); print_matrix (a); System ("pause"); Return 0 ;}