Problem 1433. Mirror Image matrix across anti-diagonal

Given an input number x, create a mirror image matrix 'Y' across the anti-diagonal. For example, if x=3,

 Y = [1 2 3;
      2 3 2;
      3 2 1]

If x=4,

 Y = [1 2 3 4;
      2 3 4 3;
      3 4 3 2;
      4 3 2 1]