Customer Revenue and Referral Tracking: Get Lowest K by Total Revenue Threshold

Problem: Customer Revenue and Referral Tracking (Lowest K above a threshold) Design a data structure to manage customers and their revenue, with an optional referrer relationship. Implement the following APIs: int insertNewCustomer(double revenue) Insert a new customer with initial spending revenue. Return a unique customerId. int insertNewCustomer(double revenue, int referrerId) Insert a new customer with initial spending revenue and a given referrerId. Return a unique customerId. Set<Integer> getLowestK(int k, double minTotalRevenue) Return up to k customer IDs whose total revenue contribution satisfies: totalRevenue >= minTotalRevenue among all customers meeting the threshold, they have the smallest totalRevenue (take the first k in ascending order) Return type is a Set<Integer>. Note: The interview notes do not specify what exactly totalRevenue means or whether referrals change revenue accumulation (e.g., referral commission along the chain). Clarify with the interviewer. Example insertNewCustomer(10) -> 0 insertNewCustomer(30, 0) -> 1 insertNewCustomer(50, 1) -> 2 getLowestK(1, 45) -> {2} getLowestK(2, 45) -> {1, 2} Example Input insertNewCustomer(10) insertNewCustomer(30,0) insertNewCustomer(50,1) getLowestK(1,45) Output {2}