Design a data structure that supports insertion, deletion, and random element retrieval, all in constant time on average. You'll need to handle edge cases carefully to achieve O(1) complexity.

You are given an array representing the heights of vertical lines. Find two lines that, together with the x-axis, form a container that holds the most water.

You are given a list of meeting time intervals. Determine the minimum number of conference rooms required to accommodate all the meetings without any overlap.