Given an $m \times n$ integer matrix mat, return a list containing all elements of mat traversed in diagonal order.

In diagonal traversal, the diagonals alternate between moving upward-right and downward-left across the matrix, visiting every element exactly once.

Constraints:

• m $==$ mat.length

• n $==$ mat[i].length

• $1 \leq$ m, n $\leq 10^4$

• $1 \leq$ m $*$ n $\leq 10^4$

• $-10^5 \leq$ mat[i][j] $\leq 10^5$

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.