LeetCode_Rotate Image

You are given an n x n 2D matrix representing an image.

Rotate the image by 90 degrees (clockwise).

Follow up:
Could you do this in-place?

The rotation can be performed in layers, where you perform a cyclic swap on the edges on 

each layer In the frst for loop, we rotate the frst layer (outermost edges) We rotate the
edges by doing a four-way swap frst on the corners, then on the element clockwise from the
edges, then on the element three steps away
Once the exterior elements are rotated, we then rotate the interior region’s edge

class Solution {
public:
    void rotate(vector<vector<int> > &matrix) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        int n = matrix.size();
        if(n < 2) return ;
        for(int lay = 0 ; lay < n/2; lay ++){
              int first = lay ;
              int last = n - 1 - lay;
            for(int i = first; i< last; i++){
                int offset = i - first;
                //store the top
                int top = matrix[first][i] ;
                //left to top
                 matrix[first][i] = matrix[last - offset][first];
                 //bottom to left
                 matrix[last - offset][first] = matrix[last][last- offset];
                 //right to bottom
                 matrix[last][last - offset] = matrix[i][last];
                 //top to right
                 matrix[i][last] = top;        
            }
        }            
    }
};