Given an array $a$, we have to find product of $a_{j}$-$a_{i}$ modulo $998244353$ over all $i$ and $j$ given $j>i$


Given an array $ a$ , we have to find product of $ a_{j}$ $ a_{i}$ modulo $ 998244353$ over all $ i$ and $ j$ given $ j>i$ .
For eg. Let the array be $ 1,2,3$ then my answer will be calculated as-
$ (2-1)$ .$ (3-1)$ .$ (3-2)$ =$ 2$
As number of elements in the array could be large (upto $ 10^5$ ) I am looking for solution of order $ nlogn$ .
I have tried representing array as a polynomial but could get anything out of it. Please help.