Minimum Product Sum

Problem Overview

• Rearrange an array of integers to minimize a product-sum expression; the given formula uses 1-based indexing.
• Input: int arr[n]; output: long minimum product sum; implement findMinimumSum(arr).
• Constraints: 1 ≤ n ≤ 2×10^5, 1 ≤ arr[i] ≤ 10^5.
• Context: array reordering for cost minimization in optimization/scheduling domains.
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