Implement and Debug a Random Dasher Picker

Random Dasher Picker (Debugging) Implement a data structure for managing available delivery drivers (Dashers). Each Dasher has a unique integer dasherId. Support the following operations: ADD id: Add id to the available Dasher set. Print false if it already exists; otherwise insert it and print true. PICK: Select one currently available Dasher uniformly at random, print its ID, and remove it from the set. Print EMPTY when the set is empty. SIZE: Print the number of currently available Dashers. Requirements: Both ADD and a successful PICK must run in expected O(1) time. The implementation must not throw on an empty set, a one-element set, or when the removed item is already the last item. There are at most 2 * 10^5 operations, and each dasherId is a signed 32-bit integer. Explain the race conditions that can occur if ADD and PICK run concurrently, and provide one solution that preserves correctness. If Dasher availability must be confirmed by a slow upstream service, explain how to avoid indefinitely blocked requests and duplicate assignments. Input Format The first line contains integer q. Each of the next q lines is one operation: ADD id, PICK, or SIZE. Output Format Print one result per operation. Example Input: 8 PICK ADD 101 ADD 202 ADD 101 SIZE PICK SIZE PICK Output: EMPTY true true false 2 101 or 202 1 the other remaining ID The actual PICK output is random; every available Dasher must have the same probability of being selected. Example Input 1 PICK Output EMPTY