You are given two independent coding tasks. ## Task 1: Minimum total cost to reduce an array You are given an integer array `arr` of length `n`. You may repeatedly perform the following **reduction** operation until only one number remains: 1. Choose any two elements `x` and `y` currently in the array. 2. Remove both from the array. 3. Insert their sum `x + y` back into the array. 4. The **cost** of this operation is `x + y`. Return the **minimum possible total cost** over all sequences of operations. **Input:** `arr` (integers) **Output:** minimum total cost (use 64-bit integer) **Notes/assumptions (make explicit in your solution):** - `n >= 1`. - Elements can be any integers; total cost should be computed using 64-bit arithmetic. --- ## Task 2: Pair elements into equal-sum groups and sum products You are given an integer array `arr` of **even** length `2m`. You must partition the array into `m` disjoint pairs such that: - Every element is used in exactly one pair. - The **sum of the two numbers in each pair is the same constant** `S` for all pairs. If such a partition is possible, return: - The value \(\sum_{i=1}^{m} (a_i \times b_i)\), i.e., the **sum of products** of each pair. If it is **not** possible to form such pairs, return `-1`. **Input:** `arr` (even length) **Output:** sum of pairwise products, or `-1` (use 64-bit integer)