Get Max Discount Pairs

Problem Overview

• Count pairs (i, j) with i < j where price[i] + price[j] is a power of three.
• Input: array of n product prices (integers); Output: integer count of qualifying pairs.
• Context: Amazon Prime Day offer rewards pairs whose sum hits a power of three with a 50% discount.
• Source: Asked in Amazon interviews; a coding interview problem often used as an interview question.