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?

public class Solution {
    public void rotate(int[][] matrix) {
        int len = matrix.length;
        if(len<=0) return;
        for(int i=0;i<len-1;i++){
            for(int j=0;j<len-i;j++){
                swap(matrix,i,j,len-1-j,len-1-i);
            }
        }
        for(int i=0;i<len/2;i++){
            for(int j=0;j<len;j++){
                swap(matrix,i,j,len-1-i,j);
            }
        }
    }
    public void swap(int[][]matrix,int x,int y,int x2,int y2){
        int temp = matrix[x][y];
        matrix[x][y] = matrix[x2][y2];
        matrix[x2][y2] = temp;
    }
}