Clarify that duplicates are allowed and getRandom must return elements with probability proportional to frequency. Propose a hybrid data structure combining a dynamic array of elements (with duplicates) and a hash map from element to a set of indices, enabling O(1) add, delete, and getRandom by swapping with the last element. Explain how to handle duplicates by storing multiple indices per element and updating the map during swaps.
Pro tip: Mention that using a set of indices per element allows O(1) deletion even with duplicates, but if the interviewer prefers a simpler approach, you can use a list of indices and swap with the last index in that list. Also, discuss the trade-off between memory overhead and simplicity.
Confirm that duplicates are allowed, getRandom should be weighted by frequency, and all operations must be average O(1). Ask about memory constraints and whether elements can be any type.
Use a dynamic array to store all elements (including duplicates) and a hash map from element to a set (or list) of indices where it appears. This allows O(1) access and updates.
Append the element to the array, record its index in the hash map, and increment its frequency count (if needed).
To delete one occurrence of an element, retrieve an index from its set, swap that element with the last element in the array, update the index sets for both elements, and remove the last element.
Generate a random index uniformly from 0 to array length-1 and return the element at that index. Since duplicates are stored multiple times, the probability is proportional to frequency.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.