Find sum of lengths of all subarrays of an array consisting particular index of the given array?

index may be any

Any formula for this?

Bro i asked sum of lengths and not count of subarrays there is difference in both

Sorry, I misread it.

If you want to find the sum of lengths of all subarrays which contain index `k`

: Remove the sum of lengths of all subarrays which donâ€™t contain the index `k`

from the sum of lengths of all possible subarrays.

Sum of length of all subarrays for an array of size `n = cnt(n) = n * (n + 1) * (n + 2) / 6`

`finalAns = cnt(n) - (cnt(k - 1) + cnt(n - k))`

I have assumed 1-based indexing.