Leetcode in Java 48.Rotate Image

You are given an n x n 2D matrix representing an image.
Rotate the image by 90 degrees (clockwise).
Note:
You have to rotate the image in-place, which means you have to modify the input 2D matrix directly. DO NOT allocate another 2D matrix and do the rotation.

给定一个 n × n 的二维矩阵表示一个图像。
将图像顺时针旋转 90 度。
说明：
你必须在原地旋转图像，这意味着你需要直接修改输入的二维矩阵。请不要使用另一个矩阵来旋转图像。

class Solution {
    public void rotate(int[][] matrix) {
        if (matrix == null || matrix.length == 0) {
            return;
        }

        int rows = matrix.length;
        int cols = matrix[0].length;
        // Reverse top to down
        for (int i = 0; i < rows / 2; i++) {
            for (int j = 0; j < cols; j++) {
                int temp = matrix[i][j];
                matrix[i][j] = matrix[rows-i-1][j];
                matrix[rows-i-1][j] = temp;
            }
        }
        // Swap the symmetry
        for (int i = 0; i < rows; i++) {
            for (int j = i; j < cols; j++) {
                int temp = matrix[i][j];
                matrix[i][j] = matrix[j][i];
                matrix[j][i] = temp;
            }
        }
    }
}