Maximum Amount

Problem Overview

• Find the maximum revenue selling to m customers, each buying one item of any type.
• Price rule: the sale price of an item equals the current remaining count of its type at purchase time.
• Input: quantity[n] (counts per type), m; Output: long integer maximum amount.
• Constraints: n ≤ 1e5, m ≤ 1e9, quantity[i] ≤ 1e9.
• Real-world context: greedy shopkeeper pricing/inventory management; Jpmorgan coding interview problem and interview question.