Same Sum Blocks (Hard)

This problem is given in two editions, which differ exclusively in the constraints on the number $$$n$$$.

You are given an array of integers $$$a[1], a[2], \dots, a[n].$$$ A block is a sequence of contiguous (consecutive) elements $$$a[l], a[l+1], \dots, a[r]$$$ ($$$1 \le l \le r \le n$$$). Thus, a block is defined by a pair of indices $$$(l, r)$$$.

Find a set of blocks $$$(l_1, r_1), (l_2, r_2), \dots, (l_k, r_k)$$$ such that:

• They do not intersect (i.e. they are disjoint). Formally, for each pair of blocks $$$(l_i, r_i)$$$ and $$$(l_j, r_j$$$) where $$$i \neq j$$$ either $$$r_i < l_j$$$ or $$$r_j < l_i$$$.
• For each block the sum of its elements is the same. Formally, $$$$$$a[l_1]+a[l_1+1]+\dots+a[r_1]=a[l_2]+a[l_2+1]+\dots+a[r_2]=$$$$$$ $$$$$$\dots =$$$$$$ $$$$$$a[l_k]+a[l_k+1]+\dots+a[r_k].$$$$$$
• The number of the blocks in the set is maximum. Formally, there does not exist a set of blocks $$$(l_1', r_1'), (l_2', r_2'), \dots, (l_{k'}', r_{k'}')$$$ satisfying the above two requirements with $$$k' > k$$$.

The picture corresponds to the first example. Blue boxes illustrate blocks.

Write a program to find such a set of blocks.