The Top Interview 150 LeetCode List

Top Interview 150: the official interview-preparation list, a hundred and fifty problems covering every data structure and technique a technical screen is likely to reach for.

150 problems
40 Easy
92 Medium
18 Hard
21 patterns

Where this list comes from

The Top Interview 150 is not ours. It is a published selection that people work through by name, and we reproduce it here by problem number, in the order the list itself uses. What we add is the solution: of the 150 entries below, 150 carry a complete Python solution with a worked example and its time and space complexity.

The published list names 150 entries. All 150 resolve to a problem in this library and are listed below.

Every count on this page is computed from what the page renders, so the number in a heading is the number of rows under it. Nothing is padded to make a title's number come out right — that would be wrong in a way anyone who knows the list would spot in seconds.

All 150 problems, grouped by pattern

Each group is the pattern that most specifically solves those problems, so the list can be worked through a technique at a time instead of a problem at a time. Groups appear in the order the list itself introduces them.

Two Pointers (14)

#	Problem	Difficulty	Topics
88	Merge Sorted Array	Easy	Array, Two Pointers, Sorting
27	Remove Element	Easy	Array, Two Pointers
26	Remove Duplicates from Sorted Array	Easy	Array, Two Pointers
80	Remove Duplicates from Sorted Array II	Medium	Array, Two Pointers
189	Rotate Array	Medium	Array, Math, Two Pointers
151	Reverse Words in a String	Medium	Two Pointers, String
28	Find the Index of the First Occurrence in a String	Easy	Two Pointers, String, String Matching
125	Valid Palindrome	Easy	Two Pointers, String
392	Is Subsequence	Easy	Two Pointers, String, Dynamic Programming
167	Two Sum II - Input Array Is Sorted	Medium	Array, Two Pointers, Binary Search
11	Container With Most Water	Medium	Greedy, Array, Two Pointers
15	3Sum	Medium	Array, Two Pointers, Sorting
202	Happy Number	Easy	Hash Table, Math, Two Pointers
5	Longest Palindromic Substring	Medium	Two Pointers, String, Dynamic Programming

Sorting (5)

#	Problem	Difficulty	Topics
169	Majority Element	Easy	Array, Hash Table, Divide and Conquer +2
274	H-Index	Medium	Array, Counting Sort, Sorting
242	Valid Anagram	Easy	Hash Table, String, Sorting
49	Group Anagrams	Medium	Array, Hash Table, String +1
56	Merge Intervals	Medium	Array, Sorting

Dynamic Programming (9)

#	Problem	Difficulty	Topics
121	Best Time to Buy and Sell Stock	Easy	Array, Dynamic Programming
53	Maximum Subarray	Medium	Array, Divide and Conquer, Dynamic Programming
70	Climbing Stairs	Easy	Memoization, Math, Dynamic Programming
198	House Robber	Medium	Array, Dynamic Programming
120	Triangle	Medium	Array, Dynamic Programming
97	Interleaving String	Medium	String, Dynamic Programming
72	Edit Distance	Medium	String, Dynamic Programming
123	Best Time to Buy and Sell Stock III	Hard	Array, Dynamic Programming
188	Best Time to Buy and Sell Stock IV	Hard	Array, Dynamic Programming

Greedy (6)

#	Problem	Difficulty	Topics
122	Best Time to Buy and Sell Stock II	Medium	Greedy, Array, Dynamic Programming
55	Jump Game	Medium	Greedy, Array, Dynamic Programming
45	Jump Game II	Medium	Greedy, Array, Dynamic Programming
134	Gas Station	Medium	Greedy, Array
135	Candy	Hard	Greedy, Array
452	Minimum Number of Arrows to Burst Balloons	Medium	Greedy, Array, Sorting

Math and Number Theory (8)

#	Problem	Difficulty	Topics
380	Insert Delete GetRandom O(1)	Medium	Design, Array, Hash Table +2
13	Roman to Integer	Easy	Hash Table, Math, String
12	Integer to Roman	Medium	Hash Table, Math, String
9	Palindrome Number	Easy	Math
66	Plus One	Easy	Array, Math
172	Factorial Trailing Zeroes	Medium	Math
50	Pow(x, n)	Medium	Recursion, Math
149	Max Points on a Line	Hard	Geometry, Array, Hash Table +1

Prefix Sum (1)

#	Problem	Difficulty	Topics
238	Product of Array Except Self	Medium	Array, Prefix Sum

Stack (8)

#	Problem	Difficulty	Topics
42	Trapping Rain Water	Hard	Stack, Array, Two Pointers +2
20	Valid Parentheses	Easy	Stack, String
71	Simplify Path	Medium	Stack, String
155	Min Stack	Medium	Stack, Design
150	Evaluate Reverse Polish Notation	Medium	Stack, Array, Math
224	Basic Calculator	Hard	Stack, Recursion, Math +1
173	Binary Search Tree Iterator	Medium	Stack, Tree, Design +3
918	Maximum Sum Circular Subarray	Medium	Queue, Array, Divide and Conquer +2

Hash Map (7)

#	Problem	Difficulty	Topics
58	Length of Last Word	Easy	String
6	Zigzag Conversion	Medium	String
68	Text Justification	Hard	Array, String, Simulation
383	Ransom Note	Easy	Hash Table, String, Counting
205	Isomorphic Strings	Easy	Hash Table, String
290	Word Pattern	Easy	Hash Table, String
1	Two Sum	Easy	Array, Hash Table

Trie (5)

#	Problem	Difficulty	Topics
14	Longest Common Prefix	Easy	Trie, Array, String
208	Implement Trie (Prefix Tree)	Medium	Design, Trie, Hash Table +1
211	Design Add and Search Words Data Structure	Medium	Depth-First Search, Design, Trie +1
212	Word Search II	Hard	Trie, Array, String +2
139	Word Break	Medium	Trie, Memoization, Array +3

Sliding Window (5)

#	Problem	Difficulty	Topics
209	Minimum Size Subarray Sum	Medium	Array, Binary Search, Prefix Sum +1
3	Longest Substring Without Repeating Characters	Medium	Hash Table, String, Sliding Window
30	Substring with Concatenation of All Words	Hard	Hash Table, String, Sliding Window
76	Minimum Window Substring	Hard	Hash Table, String, Sliding Window
219	Contains Duplicate II	Easy	Array, Hash Table, Sliding Window

Matrix and Grid (11)

#	Problem	Difficulty	Topics
36	Valid Sudoku	Medium	Array, Hash Table, Matrix
54	Spiral Matrix	Medium	Array, Matrix, Simulation
48	Rotate Image	Medium	Array, Math, Matrix
73	Set Matrix Zeroes	Medium	Array, Hash Table, Matrix
289	Game of Life	Medium	Array, Matrix, Simulation
909	Snakes and Ladders	Medium	Breadth-First Search, Array, Matrix
427	Construct Quad Tree	Medium	Tree, Array, Divide and Conquer +1
74	Search a 2D Matrix	Medium	Array, Binary Search, Matrix
64	Minimum Path Sum	Medium	Array, Dynamic Programming, Matrix
63	Unique Paths II	Medium	Array, Dynamic Programming, Matrix
221	Maximal Square	Medium	Array, Dynamic Programming, Matrix

Union-Find (4)

#	Problem	Difficulty	Topics
128	Longest Consecutive Sequence	Medium	Union Find, Array, Hash Table
200	Number of Islands	Medium	Depth-First Search, Breadth-First Search, Union Find +2
130	Surrounded Regions	Medium	Depth-First Search, Breadth-First Search, Union Find +2
399	Evaluate Division	Medium	Depth-First Search, Breadth-First Search, Union Find +4

Other (2)

#	Problem	Difficulty	Topics
228	Summary Ranges	Easy	Array
57	Insert Interval	Medium	Array

Linked List (15)

#	Problem	Difficulty	Topics
141	Linked List Cycle	Easy	Hash Table, Linked List, Two Pointers
2	Add Two Numbers	Medium	Recursion, Linked List, Math
21	Merge Two Sorted Lists	Easy	Recursion, Linked List
138	Copy List with Random Pointer	Medium	Hash Table, Linked List
92	Reverse Linked List II	Medium	Linked List
25	Reverse Nodes in k-Group	Hard	Recursion, Linked List
19	Remove Nth Node From End of List	Medium	Linked List, Two Pointers
82	Remove Duplicates from Sorted List II	Medium	Linked List, Two Pointers
61	Rotate List	Medium	Linked List, Two Pointers
86	Partition List	Medium	Linked List, Two Pointers
146	LRU Cache	Medium	Design, Hash Table, Linked List +1
117	Populating Next Right Pointers in Each Node II	Medium	Tree, Depth-First Search, Breadth-First Search +2
114	Flatten Binary Tree to Linked List	Medium	Stack, Tree, Depth-First Search +2
148	Sort List	Medium	Linked List, Two Pointers, Divide and Conquer +2
23	Merge k Sorted Lists	Hard	Linked List, Divide and Conquer, Heap (Priority Queue) +1

Tree Traversal (18)

#	Problem	Difficulty	Topics
104	Maximum Depth of Binary Tree	Easy	Tree, Depth-First Search, Breadth-First Search +1
100	Same Tree	Easy	Tree, Depth-First Search, Breadth-First Search +1
226	Invert Binary Tree	Easy	Tree, Depth-First Search, Breadth-First Search +1
101	Symmetric Tree	Easy	Tree, Depth-First Search, Breadth-First Search +1
105	Construct Binary Tree from Preorder and Inorder Traversal	Medium	Tree, Array, Hash Table +2
106	Construct Binary Tree from Inorder and Postorder Traversal	Medium	Tree, Array, Hash Table +2
112	Path Sum	Easy	Tree, Depth-First Search, Breadth-First Search +1
129	Sum Root to Leaf Numbers	Medium	Tree, Depth-First Search, Binary Tree
124	Binary Tree Maximum Path Sum	Hard	Tree, Depth-First Search, Dynamic Programming +1
236	Lowest Common Ancestor of a Binary Tree	Medium	Tree, Depth-First Search, Binary Tree
199	Binary Tree Right Side View	Medium	Tree, Depth-First Search, Breadth-First Search +1
637	Average of Levels in Binary Tree	Easy	Tree, Depth-First Search, Breadth-First Search +1
102	Binary Tree Level Order Traversal	Medium	Tree, Breadth-First Search, Binary Tree
103	Binary Tree Zigzag Level Order Traversal	Medium	Tree, Breadth-First Search, Binary Tree
530	Minimum Absolute Difference in BST	Easy	Tree, Depth-First Search, Breadth-First Search +2
230	Kth Smallest Element in a BST	Medium	Tree, Depth-First Search, Binary Search Tree +1
98	Validate Binary Search Tree	Medium	Tree, Depth-First Search, Binary Search Tree +1
108	Convert Sorted Array to Binary Search Tree	Easy	Tree, Binary Search Tree, Array +2

Bit Manipulation (7)

#	Problem	Difficulty	Topics
222	Count Complete Tree Nodes	Easy	Bit Manipulation, Tree, Binary Search +1
67	Add Binary	Easy	Bit Manipulation, Math, String +1
190	Reverse Bits	Easy	Bit Manipulation, Divide and Conquer
191	Number of 1 Bits	Easy	Bit Manipulation, Divide and Conquer
136	Single Number	Easy	Bit Manipulation, Array
137	Single Number II	Medium	Bit Manipulation, Array
201	Bitwise AND of Numbers Range	Medium	Bit Manipulation

Breadth-First Search (4)

#	Problem	Difficulty	Topics
133	Clone Graph	Medium	Depth-First Search, Breadth-First Search, Graph +1
433	Minimum Genetic Mutation	Medium	Breadth-First Search, Hash Table, String
127	Word Ladder	Hard	Breadth-First Search, Hash Table, String
322	Coin Change	Medium	Breadth-First Search, Array, Dynamic Programming

Topological Sort (2)

#	Problem	Difficulty	Topics
207	Course Schedule	Medium	Depth-First Search, Breadth-First Search, Graph +1
210	Course Schedule II	Medium	Depth-First Search, Breadth-First Search, Graph +1

Backtracking (7)

#	Problem	Difficulty	Topics
17	Letter Combinations of a Phone Number	Medium	Hash Table, String, Backtracking
77	Combinations	Medium	Backtracking
46	Permutations	Medium	Array, Backtracking
39	Combination Sum	Medium	Array, Backtracking
52	N-Queens II	Hard	Backtracking
22	Generate Parentheses	Medium	String, Dynamic Programming, Backtracking
79	Word Search	Medium	Depth-First Search, Array, String +2

Monotonic Stack (8)

#	Problem	Difficulty	Topics
35	Search Insert Position	Easy	Array, Binary Search
162	Find Peak Element	Medium	Array, Binary Search
33	Search in Rotated Sorted Array	Medium	Array, Binary Search
34	Find First and Last Position of Element in Sorted Array	Medium	Array, Binary Search
153	Find Minimum in Rotated Sorted Array	Medium	Array, Binary Search
4	Median of Two Sorted Arrays	Hard	Array, Binary Search, Divide and Conquer
69	Sqrt(x)	Easy	Math, Binary Search
300	Longest Increasing Subsequence	Medium	Array, Binary Search, Dynamic Programming

Heap / Priority Queue (4)

#	Problem	Difficulty	Topics
215	Kth Largest Element in an Array	Medium	Array, Divide and Conquer, Quickselect +2
502	IPO	Hard	Greedy, Array, Sorting +1
373	Find K Pairs with Smallest Sums	Medium	Array, Heap (Priority Queue)
295	Find Median from Data Stream	Hard	Design, Two Pointers, Data Stream +2

Other study lists

Blind 7575 problemsThe Blind 75: a 75-problem list assembled from the patterns that keep reappearing in technical interviews, grouped by topic. Every entry links to a Python solution with complexity analysis.NeetCode 150150 problemsThe NeetCode 150: an expansion of the Blind 75 into eighteen topic groups, from arrays and hashing through advanced graphs and two-dimensional dynamic programming.Grind 7575 problemsThe Grind 75: the Blind 75 reworked into a week-by-week schedule that starts with the easiest high-yield problems and ends on the hard ones. Ordered for study, not by topic.LeetCode 7575 problemsLeetCode 75: the official study plan, seventy-five problems across twenty-two topic groups from array and string work up to monotonic stacks. Skewed easier than the Blind 75 and better as a first pass.

Or go by technique instead of by list: all LeetCode patterns · the full problem list.

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