lintcode-medium-Rotate Image

You are given an n x n 2D matrix representing an image.
Rotate the image by 90 degrees (clockwise).

Example

Given a matrix

[
    [1,2],
    [3,4]
]

rotate it by 90 degrees (clockwise), return

[
    [3,1],
    [4,2]
]

Challenge

Do it in-place.

public class Solution {
    /**
     * @param matrix: A list of lists of integers
     * @return: Void
     */
    public void rotate(int[][] matrix) {
        // write your code here

        if(matrix == null || matrix.length <= 1)
            return;

        int n = matrix.length;

        for(int i = 0; i < n / 2; i++)
            rotate(matrix, i);

        return;
    }

    public void rotate(int[][] matrix, int num){

        int n = matrix.length;

        int start = num;
        int end = n - 1 - num;

        for(int i = 0; i < end - start; i++){
            int temp = matrix[start][start + i];
            matrix[start][start + i] = matrix[end - i][start];
            matrix[end - i][start] = matrix[end][end - i];
            matrix[end][end - i] = matrix[start + i][end];
            matrix[start + i][end] = temp;
        }

        return;
    }

}