Leetcode: Rotate Image

1  2  3      7  8  9      7  4  1
4  5  6  ->  4  5  6  ->  8  5  2
7  8  9      1  2  3      9  6  3

class Solution
{
public:
    void rotate(vector<vector<int> > &matrix)
    {
        if (matrix.empty()) return;
        int rows = int(matrix.size());
        int cell = 0;
        //上下对折
        for (int i = 0; i < rows / 2; ++i)
        {
            for (int j = 0; j < rows; ++j)
            {
                cell = matrix[i][j];
                matrix[i][j] = matrix[rows - i - 1][j];
                matrix[rows - i - 1][j] = cell;
            }
        }
        //对角线对折
        for (int i = 0; i < rows; ++i)
        {
            for (int j = 0; j < i; ++j)
            {
                cell = matrix[i][j];
                matrix[i][j] = matrix[j][i];
                matrix[j][i] = cell;
            }
        }
    }
};