I am part of a tech group on Facebook. One of the members shared that PayPal had an opening, so I shared my resume. It was then shared with a recruiter at the company.

This was a one-hour phone interview: 50 minutes of coding and 10 minutes of questions. The interviewer briefly introduced himself and then got right into the technical interview.

Design and implement a data structure for a Least Recently Used (LRU) cache that supports the operations get and put.

get(key) - Get the value (will always be positive) of the key if the key exists in the cache. Otherwise, return -1.

put(key, value) - Set or insert the value if the key is not already present. When the cache reaches its capacity, it should invalidate the least recently used item before inserting a new item.

Could you do both operations in O(1) complexity?