Rotate image.java

class Solution {

  /*
  [1,2,3],
  [4,5,6],
  [7,8,9]
  mirror around secondary diagonal   
  [9, 6, 3],
  [8, 5, 2],
  [7, 4, 1]
  mirror horizontally around middle line
  [7, 4, 1],
  [8, 5, 2],
  [9, 6, 3]
  */

  /*
  [ 5, 1, 9,11],
  [ 2, 4, 8,10],
  [13, 3, 6, 7],
  [15,14,12,16]
  mirror around secondary diagonal 
  [16, 7, 10, 11],
  [12, 6,  8,  9],
  [14, 3,  4,  1],
  [15, 13, 2,  5]
  mirror horizontally around middle line
  ...
  
  */

  public void rotate(int[][] matrix) {
    mirrorSecondaryDiagonal(matrix);
    mirrorHorizontally(matrix);
  }

  private static void mirrorSecondaryDiagonal(int[][] matrix) {
        // flip second diagonaly
    for(int i = 0; i < matrix.length; i++) {
      for(int j = 0; j < matrix.length - i - 1; j++) {
        int current = matrix[i][j];
        matrix[i][j] = matrix[matrix.length - j - 1][matrix.length - i - 1];
        matrix[matrix.length - j - 1][matrix.length - i - 1] = current;
      }
    }
  }
    // flip horizontally
  private static void mirrorHorizontally(int[][] matrix) {
    for(int i = 0; i < matrix.length / 2; i++) {
      for(int j = 0; j < matrix.length; j++) {
        int current = matrix[i][j];
        matrix[i][j] = matrix[matrix.length - i - 1][j];
        matrix[matrix.length - i - 1][j] = current;
      }
    }

  }
}