PROBLEMS/OBJECT-ORIENTED DESIGN

Object-Oriented Design LeetCode Problems

Low-level / object-oriented design problems — model a system, service, or game as a stateful class. The classic "design a X" interview round: LRU Cache, Design Twitter, Parking System, Snake Game, and more. 47 problems, ranked by importance. These cut across mastery patterns — each links to where it lives on the skill tree.

#	PROBLEM	DIFF	ELO	IMP	PATTERN
1	LRU Cache	Medium	1580	93	Hash-Backed Design
2	Time Based Key-Value Store	Medium	1575	88	Boundary Finding (Bisect Left/Right)
3	Design Twitter	Medium	1533	82	Merge K Sorted Structures
4	Insert Delete GetRandom O(1)	Medium	1502	78	Hash-Backed Design
5	LFU Cache	Hard	2028	78	Hash-Backed Design
6	Stock Price Fluctuation	Hard	1832	63	Heap Simulation
7	My Calendar I	Medium	1432	62	Interval Merging
8	Design a Food Rating System	Medium	1782	62	Heap Simulation
9	Design Task Manager	Hard	1807	62	Heap Simulation
10	Design Underground System	Medium	1465	60	Hash-Backed Design
11	Design Tic-Tac-ToePREMIUM	Medium	1412	58	Frequency Counting / Hash Map Lookup
12	Design Search Autocomplete SystemPREMIUM	Hard	1937	58	Trie Construction / Prefix Search
13	My Calendar II	Medium	1580	58	Interval Merging
14	Implement Router	Hard	1851	58	Hash-Backed Design
15	Design Event Manager	Medium	1548	58	Heap Simulation
16	Design Hit CounterPREMIUM	Easy	1316	56	Hash-Backed Design
17	Seat Reservation Manager	Medium	1429	55	Heap Simulation
18	Design Auction System	Hard	1854	55	Heap Simulation
19	Insert Delete GetRandom O(1) - Duplicates allowed	Hard	1847	54	Hash-Backed Design
20	Design A LeaderboardPREMIUM	Easy	1354	52	Top-K Elements
21	Design Browser History	Medium	1454	52	Stack-Based Simulation
22	Logger Rate LimiterPREMIUM	Easy	1087	48	Hash-Backed Design
23	Design In-Memory File SystemPREMIUM	Medium	1798	48	Trie Construction / Prefix Search
24	Exam Room	Hard	2067	48	Heap Simulation
25	Design Order Management SystemPREMIUM	Medium	1620	45	Hash-Backed Design
26	Design Ride Sharing System	Medium	1594	45	Frequency Counting / Hash Map Lookup
27	Design Movie Rental System	Hard	2182	42	Heap Simulation
28	Design Video Sharing PlatformPREMIUM	Medium	1650	42	Hash-Backed Design
29	Design a Text Editor	Hard	1912	41	Stack-Based Simulation
30	Throne Inheritance	Medium	1769	40	DFS Traversal (Inorder, Preorder, Postorder)
31	Design Snake GamePREMIUM	Medium	1438	38	Frequency Counting / Hash Map Lookup
32	Design Authentication Manager	Medium	1534	38	Hash-Backed Design
33	Booking Concert Tickets in Groups	Hard	2470	38	Boundary Finding (Bisect Left/Right)
34	Design Memory Allocator	Medium	1746	38	Frequency Counting / Hash Map Lookup
35	Design an ATM Machine	Medium	1616	35	General Greedy (Greedy is main insight)
36	Design a File Sharing SystemPREMIUM	Medium	1580	33	Hash-Backed Design
37	Design Spreadsheet	Medium	1524	32	Hash-Backed Design
38	Encode and Decode TinyURL	Easy	1215	30	Frequency Counting / Hash Map Lookup
39	Design Phone DirectoryPREMIUM	Easy	1218	28	Hash-Backed Design
40	Design Excel Sum FormulaPREMIUM	Hard	2194	28	Topological Sort
41	Tweet Counts Per Frequency	Hard	2037	28	Hash-Backed Design
42	Apply Discount Every n Orders	Medium	1430	28	Frequency Counting / Hash Map Lookup
43	Walking Robot Simulation II	Hard	1919	28	Matrix Traversal (Diagonal, Valid Sudoku, etc)
44	Design a Todo ListPREMIUM	Medium	1550	28	Hash-Backed Design
45	Design Log Storage SystemPREMIUM	Medium	1548	27	Sorting + Comparison
46	Simple Bank System	Easy	1356	22	Frequency Counting / Hash Map Lookup
47	Design Parking System	Easy	1324	12	Frequency Counting / Hash Map Lookup

// your mastery

What's your Object-Oriented Design tier?

leaps.gg syncs your LeetCode history, scores your mastery of every pattern behind these problems, and recommends what to practice next with spaced repetition. Free to start.

GET MY MASTERY MAP →