Given a square matrix mat, calculate and return the sum of all elements lying on its primary diagonal and secondary diagonal.

Elements that belong to both diagonals should only be included once in the total sum.

Constraints:

• n == mat.length == mat[i].length

• $1 \le$ n $\le 100$

• $1 \le$ mat[i][j] $\le 100$

Now, let’s take a moment to make sure you’ve correctly understood the problem. The quiz below helps you check if you’re solving the correct problem:

We have a game for you to play. Rearrange the logical building blocks to develop a clearer understanding of how to solve this problem.

Implement your solution in the following coding playground.