Interview Question for Software Development Engineer at Microsoft:

I will not write the code I will just post the solution. The code is straightforward.

Observation:
- in order to talk about diagonals in a two dimensional array, that means that we are dealing with a (n x n) array (square matrix)

Solution:
- flip on the first diagonal (i = j): (i, j) <->(j, i)
- flip on the second diagonal (i + j = n): (i,j) <-> (n - j, n - i)

To write the code should be straightforward. Be careful to flip only half of the matrix :) and not all the elements!