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

Solution:

• Headache Implement question!
• Very carefully to treat index.
• Only calculate the 1/4 of index in matrix!

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

        int n = matrix.length;

        // One of i or j need to consider boundry!
        for(int i = 0; i < ( n >> 1); i ++) {
        // that's why j < (n+1) / 2, that is the boundry!
            for(int j = 0; j < ( n+1 >> 1); j++) {
                int tmp = matrix[i][j];
                matrix[i][j] = matrix[n - j - 1][i];
                matrix[n - j - 1][i] = matrix[n - i - 1][n - j - 1];
                matrix[n - i - 1][n - j - 1] = matrix[j][n - i - 1];
                matrix[j][n - i - 1] = tmp;
            }
        }
    }
}