Given an array A of N integers answer Q queries of type (L, R). Answer to a query (L, R) is the sum of distinct integers in the range A[L...R]

Constraints: N, Q <= 100000

0 <= L <= R < N

A[i] <= 1 000 000 000

I read somewhere that this can be done using persistence segment tree.

So, it would be helpful if one can explain that approach.

Other approach are welcome too.