Interview Problems

Practice coding problems with detailed solutions and explanations

Ranking	Problem	Difficulty	Companies	Topics	Frequency
#1	Two Sum	Easy	+6 more	Array Tabla Hash	95%
#2	Valid Parentheses	Easy	+6 more	Cadena Pila	89%
#3	Best Time to Buy and Sell Stock	Easy	+6 more	Array Programación Dinámica	87%
#4	Merge Two Sorted Lists	Easy	+6 more	Lista Enlazada Recursión	84%
#5	Valid Anagram	Easy	+6 more	Tabla Hash Cadena +1 more	82%
#6	Binary Search	Easy	+6 more	Array Búsqueda Binaria	80%
#7	Reverse Linked List	Easy	+6 more	Lista Enlazada Recursión	78%
#8	Contains Duplicate	Easy	+6 more	Array Tabla Hash +1 more	76%
#9	Maximum Subarray	Medium	+6 more	Array Divide y Vencerás +1 more	74%
#10	3Sum	Medium	+6 more	Array Dos Punteros +1 more	72%
#11	Climbing Stairs	Easy	+6 more	Matemáticas Programación Dinámica +1 more	70%
#12	Longest Palindromic Substring	Medium	+6 more	Cadena Programación Dinámica	68%
#13	Product of Array Except Self	Medium	+6 more	Array Suma de Prefijos	66%
#14	Group Anagrams	Medium	+6 more	Array Tabla Hash +2 more	64%
#15	Top K Frequent Elements	Medium	+6 more	Array Tabla Hash +6 more	62%
#16	Palindromic Substrings	Medium	+4 more	Cadena Programación Dinámica	68%
#17	Course Schedule	Medium	+5 more	Búsqueda en Profundidad Búsqueda en Amplitud +2 more	75%
#18	House Robber	Medium	+5 more	Array Programación Dinámica	82%
#19	Meeting Rooms II	Medium	+6 more	Array Dos Punteros +3 more	88%
#20	Implement Trie (Prefix Tree)	Medium	+6 more	Tabla Hash Cadena +2 more	79%
#21	Lowest Common Ancestor of a Binary Tree	Medium	+6 more	Árbol Búsqueda en Profundidad +1 more	85%
#22	Word Search	Medium	+6 more	Array Backtracking +1 more	77%
#23	Subarray Sum Equals K	Medium	+6 more	Array Tabla Hash +1 more	81%
#24	Spiral Matrix	Medium	+6 more	Array Matriz +1 more	73%
#25	Decode Ways	Medium	+6 more	Cadena Programación Dinámica	69%
#26	Find Minimum in Rotated Sorted Array	Medium	+6 more	Array Búsqueda Binaria	84%
#27	Kth Largest Element in an Array	Medium	+6 more	Array Divide y Vencerás +3 more	91%
#28	Combination Sum	Medium	+6 more	Array Backtracking	78%
#29	Number of Islands	Medium	+6 more	Array Búsqueda en Profundidad +3 more	89%
#30	Longest Substring Without Repeating Characters	Medium	+6 more	Tabla Hash Cadena +1 more	93%
#31	Container With Most Water	Medium	+6 more	Array Dos Punteros +1 more	86%
#32	Merge Intervals	Medium	+6 more	Array Ordenación	87%
#33	Rotate Array	Medium	+6 more	Array Matemáticas +1 more	72%
#34	Search in Rotated Sorted Array	Medium	+6 more	Array Búsqueda Binaria	88%
#35	Permutations	Medium	+6 more	Array Backtracking	79%
#36	Jump Game	Medium	+6 more	Array Programación Dinámica +1 more	83%
#37	Unique Paths	Medium	+6 more	Matemáticas Programación Dinámica +1 more	76%
#38	Set Matrix Zeroes	Medium	+6 more	Array Tabla Hash +1 more	71%
#39	Minimum Window Substring	Hard	+6 more	Tabla Hash Cadena +1 more	85%
#40	Coin Change	Medium	+6 more	Array Programación Dinámica +1 more	90%
#41	Word Break	Medium	+6 more	Tabla Hash Cadena +2 more	83%
#42	Longest Common Subsequence	Medium	+6 more	String Dynamic Programming	81%
#43	Edit Distance	Medium	+6 more	String Dynamic Programming	77%
#44	Trapping Rain Water	Hard	+6 more	Array Two Pointers +2 more	92%
#45	Clone Graph	Medium	+6 more	Hash Table Depth-First Search +2 more	78%
#46	Pacific Atlantic Water Flow	Medium	+6 more	Array Depth-First Search +2 more	71%
#47	Alien Dictionary	Hard	+6 more	Array String +4 more	74%
#48	Graph Valid Tree	Medium	+6 more	Depth-First Search Breadth-First Search +2 more	69%
#49	Number of Connected Components	Medium	+6 more	Depth-First Search Breadth-First Search +2 more	76%
#50	Longest Increasing Subsequence	Medium	+6 more	Array Binary Search +1 more	84%
#54	Maximum Depth of Binary Tree	Easy	+6 more	Tree Depth-First Search +2 more	85%
#55	Same Tree	Easy	+6 more	Tree Depth-First Search +2 more	82%
#56	Symmetric Tree	Easy	+6 more	Tree Depth-First Search +2 more	80%
#57	Path Sum	Easy	+6 more	Tree Depth-First Search +2 more	78%
#58	Minimum Depth of Binary Tree	Easy	+6 more	Tree Depth-First Search +2 more	76%
#59	Balanced Binary Tree	Easy	+6 more	Tree Depth-First Search +1 more	74%
#60	Convert Sorted Array to Binary Search Tree	Easy	+6 more	Array Divide and Conquer +3 more	72%
#62	Remove Duplicates from Sorted List	Easy	+6 more	Linked List	68%
#63	Linked List Cycle	Easy	+6 more	Hash Table Linked List +1 more	66%
#64	Binary Tree Inorder Traversal	Easy	+6 more	Stack Tree +2 more	64%
#66	Binary Tree Level Order Traversal	Medium	+6 more	Tree Breadth-First Search +1 more	60%
#67	Binary Tree Zigzag Level Order Traversal	Medium	+6 more	Tree Breadth-First Search +1 more	58%
#68	Construct Binary Tree from Preorder and Inorder Traversal	Medium	+6 more	Array Hash Table +3 more	56%
#69	Populating Next Right Pointers in Each Node	Medium	+6 more	Tree Depth-First Search +2 more	54%
#70	Sum of Left Leaves	Easy	+6 more	Tree Depth-First Search +2 more	52%
#71	Find All Anagrams in a String	Medium	+6 more	Hash Table String +1 more	50%
#72	Permutation in String	Medium	+6 more	Hash Table Two Pointers +2 more	48%
#75	Sliding Window Maximum	Hard	+6 more	Array Queue +3 more	42%
#76	Single Number	Easy	+1 more	Array Bit Manipulation	85%
#77	Number of 1 Bits	Easy		Bit Manipulation Divide and Conquer	70%
#78	Counting Bits	Easy		Dynamic Programming Bit Manipulation	68%
#79	Sum of Two Integers	Medium		Math Bit Manipulation	60%
#80	Gas Station	Medium		Array Greedy	75%
#81	Partition Labels	Medium		Hash Table String +2 more	72%
#82	Task Scheduler	Medium		Array Hash Table +4 more	80%
#83	Jump Game II	Medium		Array Dynamic Programming +1 more	78%
#84	Hand of Straights	Medium		Array Hash Table +2 more	65%
#85	Min Stack	Medium		Stack Design	88%
#86	Daily Temperatures	Medium		Array Stack +1 more	82%
#87	Largest Rectangle in Histogram	Hard		Array Stack +1 more	75%
#88	Merge K Sorted Lists	Hard	+1 more	Linked List Divide and Conquer +2 more	90%
#89	Find Median from Data Stream	Hard		Two Pointers Design +3 more	85%
#90	K Closest Points to Origin	Medium		Array Math +5 more	83%
#91	Insert Interval	Medium		Array	88%
#92	Non-overlapping Intervals	Medium		Array Dynamic Programming +2 more	78%
#93	Meeting Rooms	Easy		Array Sorting	70%
#94	Design Add and Search Words Data Structure	Medium		String Depth-First Search +2 more	75%
#95	Word Search II	Hard		Array String +3 more	80%
#96	Maximum Subarray Circular	Medium	+2 more	Array Programación Dinámica +2 more	65%
#97	Median of Two Sorted Arrays	Hard	+1 more	Binary Search Divide and Conquer +1 more	85%
#98	Regular Expression Matching	Hard	+1 more	Dynamic Programming String +1 more	78%
#99	Trapping Rain Water II	Hard		Heap Matrix +1 more	72%
#100	N-Queens II	Hard		Backtracking Array	68%
#101	Word Ladder II	Hard		BFS Backtracking +1 more	65%
#102	Burst Balloons	Hard		Dynamic Programming Array	70%
#103	Sudoku Solver	Hard	+1 more	Backtracking Matrix +1 more	75%
#104	Longest Increasing Path in a Matrix	Hard		DFS Memoization +1 more	73%
#105	Palindrome Partitioning II	Hard		Dynamic Programming String	67%
#106	Max Points on a Line	Hard		Array Hash Table +2 more	64%
#107	Wildcard Matching	Hard		Dynamic Programming String +1 more	71%
#109	Word Break II	Hard		Backtracking Trie +2 more	69%
#110	Binary Tree Maximum Path Sum	Hard		Tree DFS	83%
#111	Serialize and Deserialize Binary Tree	Hard		Tree DFS +1 more	80%
#113	First Missing Positive	Hard		Array Hash Table	74%
#114	Minimum Number of K Consecutive Bit Flips	Hard		Greedy Sliding Window	62%
#115	Maximal Rectangle	Hard		Stack Matrix +1 more	70%
#116	Count of Smaller Numbers After Self	Hard		Binary Indexed Tree Merge Sort +1 more	68%
#117	Move Pieces to Obtain a String	Medium		Two Pointers String	72%
#118	Maximum Running Time of n Computers	Hard		Binary Search Array +1 more	65%
#119	LRU Cache	Medium		Hash Table Linked List +1 more	90%
#120	Longest Consecutive Sequence	Medium	B	Array Hash Table +1 more	82%
#121	Course Schedule II	Medium		Graph Topological Sort +1 more	78%
#122	Design Hit Counter	Medium		Design Queue	70%
#123	Logger Rate Limiter	Easy		Hash Table Design	72%
#124	Invert Binary Tree	Easy	+1 more	Tree Depth-First Search +2 more	88%
#125	Validate Binary Search Tree	Medium	+1 more	Tree Depth-First Search +2 more	85%
#126	Kth Smallest Element in a BST	Medium		Tree Depth-First Search +1 more	82%
#127	Subsets	Medium	+1 more	Array Backtracking +1 more	80%
#128	Rotting Oranges	Medium		Array Breadth-First Search +1 more	78%
#129	Reorder List	Medium		Linked List Two Pointers +1 more	76%
#130	House Robber II	Medium		Array Dynamic Programming	77%
#131	Maximum Product Subarray	Medium		Array Dynamic Programming	79%
#132	Koko Eating Bananas	Medium		Array Binary Search	81%
#133	Network Delay Time	Medium		Graph Shortest Path +1 more	74%
#134	Los Filósofos Comensales	Medium		Concurrency Synchronization	75%
#135	FizzBuzz Multithreaded	Medium	F	Concurrency Multithreading +1 more	75%
#136	Valid Palindrome	Easy	+2 more	Two Pointers String	90%
#137	Two Sum II - Input Array Is Sorted	Medium	+1 more	Array Two Pointers +1 more	85%
#138	Sort Colors	Medium	+1 more	Array Two Pointers +1 more	80%
#139	Missing Number	Easy	+1 more	Array Math +1 more	82%
#140	Move Zeroes	Easy	F +1 more	Array Two Pointers	78%
#141	Majority Element	Easy	+2 more	Array Hash Table +1 more	82%
#142	Diameter of Binary Tree	Easy	+1 more	Tree DFS +1 more	82%
#143	Letter Combinations of a Phone Number	Medium	+2 more	Hash Table String +1 more	82%
#144	Remove Nth Node From End of List	Medium	+1 more	Linked List Two Pointers	80%
#145	Intersection of Two Linked Lists	Easy	+1 more	Hash Table Linked List +1 more	75%
#146	Best Time to Buy and Sell Stock II	Medium	+1 more	Array Dynamic Programming +1 more	74%
#147	Flatten Binary Tree to Linked List	Medium		Linked List Stack +2 more	72%
#148	Linked List Cycle II	Medium	+1 more	Hash Table Linked List +1 more	73%
#149	First Bad Version	Easy	F +1 more	Binary Search Interactive	72%
#150	Squares of a Sorted Array	Easy		Array Two Pointers +1 more	70%
#151	Reverse Integer	Medium	+1 more	Math	72%
#152	Happy Number	Easy		Hash Table Math +1 more	71%
#153	Plus One	Easy	+1 more	Array Math	69%
#154	Pascal's Triangle	Easy		Array Dynamic Programming	68%
#155	Find All Numbers Disappeared in an Array	Easy	+1 more	Array Hash Table	68%
#156	Minimum Cost to Connect All Points	Hard	F	Array Union Find +2 more	72%
#157	Word Ladder	Hard	F +1 more	Hash Table String +1 more	82%
#158	Longest Valid Parentheses	Hard	G	String Dynamic Programming +1 more	78%
#159	The Skyline Problem	Hard	T	Array Divide and Conquer +2 more	72%
#160	Dungeon Game	Hard		Array Dynamic Programming +1 more	68%
#161	Basic Calculator	Hard	F	Math String +2 more	76%
#162	Russian Doll Envelopes	Hard		Array Binary Search +2 more	70%
#163	Reconstruct Itinerary	Hard	F	Depth-First Search Graph +1 more	68%
#164	Swim in Rising Water	Hard		Array Binary Search +3 more	65%
#165	Minimum Cost to Hire K Workers	Hard	G	Array Greedy +2 more	62%
#166	Strange Printer	Hard		String Dynamic Programming	58%
#167	Decode Ways II	Hard	F	String Dynamic Programming	64%
#168	Shortest Path in a Grid with Obstacles Elimination	Hard		Array BFS +1 more	67%
#169	Smallest Range Covering Elements from K Lists	Hard	S	Array Hash Table +4 more	60%
#170	Minimum Number of Refueling Stops	Hard	D	Array Dynamic Programming +2 more	65%
#171	Number of Atoms	Hard		Hash Table String +2 more	58%
#172	Remove Boxes	Hard	A	Array Dynamic Programming +1 more	52%
#173	Maximum Profit in Job Scheduling	Hard	D	Array Binary Search +2 more	71%
#174	Minimum Window Subsequence	Hard	F B	String Dynamic Programming +1 more	60%
#175	LFU Cache	Hard	O	Hash Table Linked List +2 more	68%
#176	Producer-Consumer con Threading	Medium		Concurrency Threading +1 more	78%
#177	Singleton Thread-Safe	Medium		Concurrency Design Patterns +1 more	72%
#178	Llamadas HTTP en Paralelo con asyncio	Medium	S	Async Programming REST API +1 more	82%
#179	Retry con Exponential Backoff	Medium	S	REST API Error Handling +1 more	85%
#180	Paginacion Automatica de API REST	Easy	G S T S	REST API Pagination +1 more	80%
#181	Flatten JSON Anidado	Easy	P D S	Recursion JSON +1 more	76%
#182	Deep Merge de Diccionarios JSON	Easy	P D S	Recursion JSON +1 more	72%
#183	Rate Limiter con Token Bucket	Medium	C S	System Design Concurrency +1 more	80%
#184	Validar y Transformar Respuesta de API	Medium	S	JSON Data Validation +1 more	78%
#185	Parser de Expresiones Aritmeticas	Hard	B	Stack String +1 more	68%
#186	Parser de Fichero de Logs	Hard	C S	File I/O Parsing +2 more	82%
#187	Organigrama Recursivo (Org Chart)	Medium	W	Tree Recursion +3 more	85%
#188	Cache Durable con WAL y Concurrencia	Hard	A R P C	Concurrency File I/O +3 more	88%
#189	Servidor HTTP con Rate Limiting y Filtrado Concurrente	Hard	C S	Concurrency Rate Limiting +3 more	79%
#190	Time-Based Key-Value Store	Medium	+1 more	Hash Map Binary Search +1 more	86%
#191	Snapshot Array	Medium	D	Binary Search Design +1 more	78%
#192	In-Memory DB con TTL e Historial	Hard	A S P	Design Hash Map +2 more	84%
#193	BPE Tokenizer	Hard	A G H	String Greedy +2 more	71%
#194	Bloom Filter	Medium	C D F +2 more	Hash Map Bit Manipulation +1 more	75%
#195	Consistent Hashing Ring	Hard	D D +2 more	Design Hash Map +1 more	80%
#196	Skip List	Hard	R	Design Linked List +1 more	65%
#197	Thread-Safe Bounded Queue (Producer-Consumer)	Medium	A +1 more	Concurrency Threading +1 more	83%
#198	Idempotent Payment Processor	Hard	S B P S +1 more	Design Concurrency +1 more	77%
#199	Webhook con Retry y Exponential Backoff	Medium	S G S +1 more	Design Concurrency +2 more	72%
#200	DAG Task Scheduler	Hard	D A +2 more	Graph Topological Sort +2 more	81%
#201	Circular Ring Buffer (Lock-Free)	Hard	S I N Q +1 more	Design Concurrency +1 more	68%
#202	LLM Context Window Manager	Hard	A G M +1 more	Design String +1 more	76%
#203	Distributed Sliding Window Rate Limiter	Hard	S C G +2 more	Sliding Window Design +2 more	88%
#204	Inference Request Batching Scheduler	Hard	A G N +1 more	Design Concurrency +2 more	79%
#205	IP Subnet Calculator	Medium	C C N +1 more	Bit Manipulation Math +1 more	66%
#206	Event Loop con Microtasks y Macrotasks	Hard	C V +1 more	Design Concurrency +1 more	70%
#207	GPU Memory Coalescing Simulator	Hard	N A I +1 more	Simulation Bit Manipulation +1 more	62%
#208	KV Store Serialization con Delimitadores Arbitrarios	Medium	D	String Design +1 more	74%
#209	Connect 4 (Juego de Tablero)	Medium	Y D T +1 more	Matrix Simulation +1 more	73%
#210	Mini Git Object Store	Hard	S C	Design Hash Map +2 more	72%
#211	Spreadsheet con Dependencias y Fórmulas	Hard	P N A	Design DAG +2 more	78%
#212	Real-time Leaderboard con Ventanas Temporales	Hard	T R +1 more	Design Heap +2 more	80%
#213	Autocomplete con Frecuencia y Typo Tolerance	Hard		Trie Design +2 more	85%
#214	HTTP Server desde Cero con Middleware	Hard	C S	Design Parsing +2 more	70%
#215	Memory Allocator con Coalescing	Hard	A N +1 more	Design Bit Manipulation +2 more	65%
#216	Text Diff y Three-Way Merge	Hard	G G A	Dynamic Programming Two Pointers +1 more	68%
#217	Distributed Job Scheduler con DAG y Workers	Hard	+1 more	Design Graphs +2 more	82%
#218	MVCC - Multi-Version Concurrency Control	Hard	P G S P	Design Concurrency +2 more	70%
#219	Mini Regex Engine con NFA	Hard		Dynamic Programming NFA +2 more	75%
#220	Event Sourcing con Snapshots y Proyecciones	Hard	S S A C	Design Event-Driven +2 more	68%

Interview Problems

Two Sum

Valid Parentheses

Best Time to Buy and Sell Stock

Merge Two Sorted Lists

Valid Anagram

Binary Search

Reverse Linked List

Contains Duplicate

Maximum Subarray

3Sum

Climbing Stairs

Longest Palindromic Substring

Product of Array Except Self

Group Anagrams

Top K Frequent Elements

Palindromic Substrings

Course Schedule

House Robber

Meeting Rooms II

Implement Trie (Prefix Tree)

Lowest Common Ancestor of a Binary Tree

Word Search

Subarray Sum Equals K

Spiral Matrix

Decode Ways

Find Minimum in Rotated Sorted Array

Kth Largest Element in an Array

Combination Sum

Number of Islands

Longest Substring Without Repeating Characters

Container With Most Water

Merge Intervals

Rotate Array

Search in Rotated Sorted Array

Permutations

Jump Game

Unique Paths

Set Matrix Zeroes

Minimum Window Substring

Coin Change

Word Break

Longest Common Subsequence

Edit Distance

Trapping Rain Water

Clone Graph

Pacific Atlantic Water Flow

Alien Dictionary

Graph Valid Tree

Number of Connected Components

Longest Increasing Subsequence

Maximum Depth of Binary Tree

Same Tree

Symmetric Tree

Path Sum

Minimum Depth of Binary Tree

Balanced Binary Tree

Convert Sorted Array to Binary Search Tree

Remove Duplicates from Sorted List

Linked List Cycle

Binary Tree Inorder Traversal

Binary Tree Level Order Traversal

Binary Tree Zigzag Level Order Traversal

Construct Binary Tree from Preorder and Inorder Traversal

Populating Next Right Pointers in Each Node

Sum of Left Leaves

Find All Anagrams in a String

Permutation in String

Sliding Window Maximum

Single Number

Number of 1 Bits

Counting Bits

Sum of Two Integers

Gas Station

Partition Labels

Task Scheduler

Jump Game II

Hand of Straights

Min Stack

Daily Temperatures