Write a method to rotate the image by 90 degree.(In place operation is required).

Let say you have an image represented by an  NXN matrix where each pixel in the image is 4 byte.So rotate this image in place by 90 degree.

 Solution:

public void rotate(int[][] matrix ,in n)
{
  for(int layer = 0, layer < n/2; ++layer)
  {
    int first =layer;
    int last =n-1-layer;
    for(int i=first;i < last; ++i)
    {
      int offset = i- first;
      int top=matrix[first][i];  //save top
      matrix[first][i]=matrix[last-offset][first];// left-top
      matrix[last-offset][first]=matrix[last][last - offset]; //bottom-left
      matrix[last][last - offset] = matrix[i][last];  //right - bottom
      matrix[i][last] =top;  //top-right
    }
  }
}

Complexity: o(n^2) because any algorithm must touch all N^2 element.

if you see closely what i am doing is:

Follow this-

1. for i=0 to n

2.temp=top[i];

3.top[i]=left[i];

4.left[i]=bottom[i];

5.bottom[i] = right[i];

6.right[i]  = temp;

we are performing swap on each layer.starting from outer most layer and working our way inwards.