The Top Interview 150 LeetCode List

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

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Easy: 40
Medium: 92
Hard: 18
Patterns: 21

Every entry, 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)

Two Pointers
No.	Problem	Difficulty	Topics
0088	Merge Sorted Array	Easy	Array, Two Pointers, Sorting
0027	Remove Element	Easy	Array, Two Pointers
0026	Remove Duplicates from Sorted Array	Easy	Array, Two Pointers
0080	Remove Duplicates from Sorted Array II	Medium	Array, Two Pointers
0189	Rotate Array	Medium	Array, Math, Two Pointers
0151	Reverse Words in a String	Medium	Two Pointers, String
0028	Find the Index of the First Occurrence in a String	Easy	Two Pointers, String, String Matching
0125	Valid Palindrome	Easy	Two Pointers, String
0392	Is Subsequence	Easy	Two Pointers, String, Dynamic Programming
0167	Two Sum II - Input Array Is Sorted	Medium	Array, Two Pointers, Binary Search
0011	Container With Most Water	Medium	Greedy, Array, Two Pointers
0015	3Sum	Medium	Array, Two Pointers, Sorting
0202	Happy Number	Easy	Hash Table, Math, Two Pointers
0005	Longest Palindromic Substring	Medium	Two Pointers, String, Dynamic Programming

Sorting (5)

Sorting
No.	Problem	Difficulty	Topics
0169	Majority Element	Easy	Array, Hash Table, Divide and Conquer +2
0274	H-Index	Medium	Array, Counting Sort, Sorting
0242	Valid Anagram	Easy	Hash Table, String, Sorting
0049	Group Anagrams	Medium	Array, Hash Table, String +1
0056	Merge Intervals	Medium	Array, Sorting

Dynamic Programming (9)

Dynamic Programming
No.	Problem	Difficulty	Topics
0121	Best Time to Buy and Sell Stock	Easy	Array, Dynamic Programming
0053	Maximum Subarray	Medium	Array, Divide and Conquer, Dynamic Programming
0070	Climbing Stairs	Easy	Memoization, Math, Dynamic Programming
0198	House Robber	Medium	Array, Dynamic Programming
0120	Triangle	Medium	Array, Dynamic Programming
0097	Interleaving String	Medium	String, Dynamic Programming
0072	Edit Distance	Medium	String, Dynamic Programming
0123	Best Time to Buy and Sell Stock III	Hard	Array, Dynamic Programming
0188	Best Time to Buy and Sell Stock IV	Hard	Array, Dynamic Programming

Greedy (6)

Greedy
No.	Problem	Difficulty	Topics
0122	Best Time to Buy and Sell Stock II	Medium	Greedy, Array, Dynamic Programming
0055	Jump Game	Medium	Greedy, Array, Dynamic Programming
0045	Jump Game II	Medium	Greedy, Array, Dynamic Programming
0134	Gas Station	Medium	Greedy, Array
0135	Candy	Hard	Greedy, Array
0452	Minimum Number of Arrows to Burst Balloons	Medium	Greedy, Array, Sorting

Math and Number Theory (8)

Math and Number Theory
No.	Problem	Difficulty	Topics
0380	Insert Delete GetRandom O(1)	Medium	Design, Array, Hash Table +2
0013	Roman to Integer	Easy	Hash Table, Math, String
0012	Integer to Roman	Medium	Hash Table, Math, String
0009	Palindrome Number	Easy	Math
0066	Plus One	Easy	Array, Math
0172	Factorial Trailing Zeroes	Medium	Math
0050	Pow(x, n)	Medium	Recursion, Math
0149	Max Points on a Line	Hard	Geometry, Array, Hash Table +1

Prefix Sum (1)

Prefix Sum
No.	Problem	Difficulty	Topics
0238	Product of Array Except Self	Medium	Array, Prefix Sum

Stack (8)

Stack
No.	Problem	Difficulty	Topics
0042	Trapping Rain Water	Hard	Stack, Array, Two Pointers +2
0020	Valid Parentheses	Easy	Stack, String
0071	Simplify Path	Medium	Stack, String
0155	Min Stack	Medium	Stack, Design
0150	Evaluate Reverse Polish Notation	Medium	Stack, Array, Math
0224	Basic Calculator	Hard	Stack, Recursion, Math +1
0173	Binary Search Tree Iterator	Medium	Stack, Tree, Design +3
0918	Maximum Sum Circular Subarray	Medium	Queue, Array, Divide and Conquer +2

Other (5)

Other
No.	Problem	Difficulty	Topics
0058	Length of Last Word	Easy	String
0006	Zigzag Conversion	Medium	String
0068	Text Justification	Hard	Array, String, Simulation
0228	Summary Ranges	Easy	Array
0057	Insert Interval	Medium	Array

Trie (5)

Trie
No.	Problem	Difficulty	Topics
0014	Longest Common Prefix	Easy	Trie, Array, String
0208	Implement Trie (Prefix Tree)	Medium	Design, Trie, Hash Table +1
0211	Design Add and Search Words Data Structure	Medium	Depth-First Search, Design, Trie +1
0212	Word Search II	Hard	Trie, Array, String +2
0139	Word Break	Medium	Trie, Memoization, Array +3

Sliding Window (5)

Sliding Window
No.	Problem	Difficulty	Topics
0209	Minimum Size Subarray Sum	Medium	Array, Binary Search, Prefix Sum +1
0003	Longest Substring Without Repeating Characters	Medium	Hash Table, String, Sliding Window
0030	Substring with Concatenation of All Words	Hard	Hash Table, String, Sliding Window
0076	Minimum Window Substring	Hard	Hash Table, String, Sliding Window
0219	Contains Duplicate II	Easy	Array, Hash Table, Sliding Window

Matrix and Grid (11)

Matrix and Grid
No.	Problem	Difficulty	Topics
0036	Valid Sudoku	Medium	Array, Hash Table, Matrix
0054	Spiral Matrix	Medium	Array, Matrix, Simulation
0048	Rotate Image	Medium	Array, Math, Matrix
0073	Set Matrix Zeroes	Medium	Array, Hash Table, Matrix
0289	Game of Life	Medium	Array, Matrix, Simulation
0909	Snakes and Ladders	Medium	Breadth-First Search, Array, Matrix
0427	Construct Quad Tree	Medium	Tree, Array, Divide and Conquer +1
0074	Search a 2D Matrix	Medium	Array, Binary Search, Matrix
0064	Minimum Path Sum	Medium	Array, Dynamic Programming, Matrix
0063	Unique Paths II	Medium	Array, Dynamic Programming, Matrix
0221	Maximal Square	Medium	Array, Dynamic Programming, Matrix

Hash Map (4)

Hash Map
No.	Problem	Difficulty	Topics
0383	Ransom Note	Easy	Hash Table, String, Counting
0205	Isomorphic Strings	Easy	Hash Table, String
0290	Word Pattern	Easy	Hash Table, String
0001	Two Sum	Easy	Array, Hash Table

Union-Find (4)

Union-Find
No.	Problem	Difficulty	Topics
0128	Longest Consecutive Sequence	Medium	Union Find, Array, Hash Table
0200	Number of Islands	Medium	Depth-First Search, Breadth-First Search, Union Find +2
0130	Surrounded Regions	Medium	Depth-First Search, Breadth-First Search, Union Find +2
0399	Evaluate Division	Medium	Depth-First Search, Breadth-First Search, Union Find +4

Linked List (15)

Linked List
No.	Problem	Difficulty	Topics
0141	Linked List Cycle	Easy	Hash Table, Linked List, Two Pointers
0002	Add Two Numbers	Medium	Recursion, Linked List, Math
0021	Merge Two Sorted Lists	Easy	Recursion, Linked List
0138	Copy List with Random Pointer	Medium	Hash Table, Linked List
0092	Reverse Linked List II	Medium	Linked List
0025	Reverse Nodes in k-Group	Hard	Recursion, Linked List
0019	Remove Nth Node From End of List	Medium	Linked List, Two Pointers
0082	Remove Duplicates from Sorted List II	Medium	Linked List, Two Pointers
0061	Rotate List	Medium	Linked List, Two Pointers
0086	Partition List	Medium	Linked List, Two Pointers
0146	LRU Cache	Medium	Design, Hash Table, Linked List +1
0117	Populating Next Right Pointers in Each Node II	Medium	Tree, Depth-First Search, Breadth-First Search +2
0114	Flatten Binary Tree to Linked List	Medium	Stack, Tree, Depth-First Search +2
0148	Sort List	Medium	Linked List, Two Pointers, Divide and Conquer +2
0023	Merge k Sorted Lists	Hard	Linked List, Divide and Conquer, Heap (Priority Queue) +1

Tree Traversal (18)

Tree Traversal
No.	Problem	Difficulty	Topics
0104	Maximum Depth of Binary Tree	Easy	Tree, Depth-First Search, Breadth-First Search +1
0100	Same Tree	Easy	Tree, Depth-First Search, Breadth-First Search +1
0226	Invert Binary Tree	Easy	Tree, Depth-First Search, Breadth-First Search +1
0101	Symmetric Tree	Easy	Tree, Depth-First Search, Breadth-First Search +1
0105	Construct Binary Tree from Preorder and Inorder Traversal	Medium	Tree, Array, Hash Table +2
0106	Construct Binary Tree from Inorder and Postorder Traversal	Medium	Tree, Array, Hash Table +2
0112	Path Sum	Easy	Tree, Depth-First Search, Breadth-First Search +1
0129	Sum Root to Leaf Numbers	Medium	Tree, Depth-First Search, Binary Tree
0124	Binary Tree Maximum Path Sum	Hard	Tree, Depth-First Search, Dynamic Programming +1
0236	Lowest Common Ancestor of a Binary Tree	Medium	Tree, Depth-First Search, Binary Tree
0199	Binary Tree Right Side View	Medium	Tree, Depth-First Search, Breadth-First Search +1
0637	Average of Levels in Binary Tree	Easy	Tree, Depth-First Search, Breadth-First Search +1
0102	Binary Tree Level Order Traversal	Medium	Tree, Breadth-First Search, Binary Tree
0103	Binary Tree Zigzag Level Order Traversal	Medium	Tree, Breadth-First Search, Binary Tree
0530	Minimum Absolute Difference in BST	Easy	Tree, Depth-First Search, Breadth-First Search +2
0230	Kth Smallest Element in a BST	Medium	Tree, Depth-First Search, Binary Search Tree +1
0098	Validate Binary Search Tree	Medium	Tree, Depth-First Search, Binary Search Tree +1
0108	Convert Sorted Array to Binary Search Tree	Easy	Tree, Binary Search Tree, Array +2

Bit Manipulation (7)

Bit Manipulation
No.	Problem	Difficulty	Topics
0222	Count Complete Tree Nodes	Easy	Bit Manipulation, Tree, Binary Search +1
0067	Add Binary	Easy	Bit Manipulation, Math, String +1
0190	Reverse Bits	Easy	Bit Manipulation, Divide and Conquer
0191	Number of 1 Bits	Easy	Bit Manipulation, Divide and Conquer
0136	Single Number	Easy	Bit Manipulation, Array
0137	Single Number II	Medium	Bit Manipulation, Array
0201	Bitwise AND of Numbers Range	Medium	Bit Manipulation

Breadth-First Search (4)

Breadth-First Search
No.	Problem	Difficulty	Topics
0133	Clone Graph	Medium	Depth-First Search, Breadth-First Search, Graph +1
0433	Minimum Genetic Mutation	Medium	Breadth-First Search, Hash Table, String
0127	Word Ladder	Hard	Breadth-First Search, Hash Table, String
0322	Coin Change	Medium	Breadth-First Search, Array, Dynamic Programming

Topological Sort (2)

Topological Sort
No.	Problem	Difficulty	Topics
0207	Course Schedule	Medium	Depth-First Search, Breadth-First Search, Graph +1
0210	Course Schedule II	Medium	Depth-First Search, Breadth-First Search, Graph +1

Backtracking (7)

Backtracking
No.	Problem	Difficulty	Topics
0017	Letter Combinations of a Phone Number	Medium	Hash Table, String, Backtracking
0077	Combinations	Medium	Backtracking
0046	Permutations	Medium	Array, Backtracking
0039	Combination Sum	Medium	Array, Backtracking
0052	N-Queens II	Hard	Backtracking
0022	Generate Parentheses	Medium	String, Dynamic Programming, Backtracking
0079	Word Search	Medium	Depth-First Search, Array, String +2

Binary Search (8)

Binary Search
No.	Problem	Difficulty	Topics
0035	Search Insert Position	Easy	Array, Binary Search
0162	Find Peak Element	Medium	Array, Binary Search
0033	Search in Rotated Sorted Array	Medium	Array, Binary Search
0034	Find First and Last Position of Element in Sorted Array	Medium	Array, Binary Search
0153	Find Minimum in Rotated Sorted Array	Medium	Array, Binary Search
0004	Median of Two Sorted Arrays	Hard	Array, Binary Search, Divide and Conquer
0069	Sqrt(x)	Easy	Math, Binary Search
0300	Longest Increasing Subsequence	Medium	Array, Binary Search, Dynamic Programming

Heap / Priority Queue (4)

Heap / Priority Queue
No.	Problem	Difficulty	Topics
0215	Kth Largest Element in an Array	Medium	Array, Divide and Conquer, Quickselect +2
0502	IPO	Hard	Greedy, Array, Sorting +1
0373	Find K Pairs with Smallest Sums	Medium	Array, Heap (Priority Queue)
0295	Find Median from Data Stream	Hard	Design, Two Pointers, Data Stream +2

The Top Interview 150 is a published third-party selection, reproduced here by problem number in the order the list itself uses. 150 of its 150 entries carry a complete Python solution.

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Technical interview · 45 minsolution.pyShared editor · Python 3Longest substring without repeatsMediumGiven a string s, return the length of the longest contiguous substring in which every character is unique.s = "abcabcbb"
→ 31def length_of_longest_substring(s: str) -> int:2 last_seen = {}3 left = best = 04 for right, ch in enumerate(s):5 if ch in last_seen and last_seen[ch] >= left:

python

def length_of_longest_substring(s: str) -> int:    last_seen = {}                    # char -> index    left = best = 0    for right, ch in enumerate(s):        if ch in last_seen and last_seen[ch] >= left:            left = last_seen[ch] + 1  # jump past it        last_seen[ch] = right        best = max(best, right - left + 1)    return best    last_seen = {}                    # char -> index

Approach

At each index r, the window's left edge is:

left r = max (left r -1, last[s r] + 1)

Time O(n): each character enters and leaves the window once.
Space O(min(n, k)): k is the size of the character set.

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python

Please analyze this context and help me answer the question or solve the problem.

python

def length_of_longest_substring(s: str) -> int:    last_seen = {}                    # char -> index    left = best = 0    for right, ch in enumerate(s):        if ch in last_seen and last_seen[ch] >= left:            left = last_seen[ch] + 1  # jump past it        last_seen[ch] = right        best = max(best, right - left + 1)    return best    last_seen = {}                    # char -> index

Approach

At each index r, the window's left edge is:

left r = max (left r -1, last[s r] + 1)

Time O(n): each character enters and leaves the window once.
Space O(min(n, k)): k is the size of the character set.

Type your message...

GPT-6.1 TerraClear chat

QuitEscHide+QCapture+PCrop+OSubmit+EnterPress to get answerLeft/Right+Up/Down+

90%Subscription

python

Please analyze this context and help me answer the question or solve the problem.

python

def length_of_longest_substring(s: str) -> int:    last_seen = {}                    # char -> index    left = best = 0    for right, ch in enumerate(s):        if ch in last_seen and last_seen[ch] >= left:            left = last_seen[ch] + 1  # jump past it        last_seen[ch] = right        best = max(best, right - left + 1)    return best    last_seen = {}                    # char -> index

Approach

At each index r, the window's left edge is:

left r = max (left r -1, last[s r] + 1)

Time O(n): each character enters and leaves the window once.
Space O(min(n, k)): k is the size of the character set.

Type your message...

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QuitEscHide+QCapture+PCrop+OSubmit+EnterPress to get answerLeft/Right+Up/Down+

Other study lists

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

Every entry, grouped by pattern

01Two Pointers (14)14

02Sorting (5)5

03Dynamic Programming (9)9

04Greedy (6)6

05Math and Number Theory (8)8

06Prefix Sum (1)1

07Stack (8)8

08Other (5)5

09Trie (5)5

10Sliding Window (5)5

11Matrix and Grid (11)11

12Hash Map (4)4

13Union-Find (4)4

14Linked List (15)15

15Tree Traversal (18)18

16Bit Manipulation (7)7

17Breadth-First Search (4)4

18Topological Sort (2)2

19Backtracking (7)7

20Binary Search (8)8

21Heap / Priority Queue (4)4

The Top Interview 150 does not cover the problem you get asked.

Approach

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Other study lists

Two Pointers (14)

Sorting (5)

Dynamic Programming (9)

Greedy (6)

Math and Number Theory (8)

Prefix Sum (1)

Stack (8)

Other (5)

Trie (5)

Sliding Window (5)

Matrix and Grid (11)

Hash Map (4)

Union-Find (4)

Linked List (15)

Tree Traversal (18)

Bit Manipulation (7)

Breadth-First Search (4)

Topological Sort (2)

Backtracking (7)

Binary Search (8)

Heap / Priority Queue (4)