Total Efficiency

Problem Overview

• Pair all participants into teams of two so each pair has the same skill sum; return the sum of team efficiencies (product of skills) or -1 if pairing is impossible.
• Input: array of integers representing skills; Output: long total efficiency; all candidates must be used; the valid total is unique.
• Context: HackerRank coding competition scenario modeling fair team formation.
• From Ibm interviews; a coding interview problem and interview question assessing pairing and aggregation understanding.