Basic

1. Sets
2. Stack
3. Queue
4. ArrayDeque
5. PriorityQueue
6. LinkedList
7. BST

Fun problems

1. Implement a Circular Queue (FIFO) using an array.
2. Implement a Stack using 2 Queues.
3. Implement a Queue using 2 Stacks.
4. Implement a Stack with getMiddle() operation in O(1).
5. Find the Kth Largest Element in a stream of integers.
6. Design a LRU Cache (get/put in constant time)
7. LRU Cache with a Frequency Counter.
8. Implement a hit counter to count hits received in the past 5 minutes.
9. Find Median from data stream. Add numbers to a data structure and find the median of the current data stream in O(log n) time.

Advanced use cases

1. Set associative array
2. Ring buffer

Probabilistic data structures

1. Hyperloglog
2. Count-min Sketch
3. Filter

• Bloom filter
• Cuckoo filter
• Quotient filter

4. T-Digest
5. Lossy counting
6. Skip list