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?

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