The Blind 75 LeetCode List

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.

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Easy: 19
Medium: 49
Hard: 7
Patterns: 20

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.

Hash Map (1)

Hash Map
No.	Problem	Difficulty	Topics
0001	Two Sum	Easy	Array, Hash Table

Dynamic Programming (10)

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
0152	Maximum Product Subarray	Medium	Array, Dynamic Programming
0070	Climbing Stairs	Easy	Memoization, Math, Dynamic Programming
1143	Longest Common Subsequence	Medium	String, Dynamic Programming
0377	Combination Sum IV	Medium	Array, Dynamic Programming
0198	House Robber	Medium	Array, Dynamic Programming
0213	House Robber II	Medium	Array, Dynamic Programming
0091	Decode Ways	Medium	String, Dynamic Programming
0062	Unique Paths	Medium	Math, Dynamic Programming, Combinatorics

Sorting (5)

Sorting
No.	Problem	Difficulty	Topics
0217	Contains Duplicate	Easy	Array, Hash Table, Sorting
0056	Merge Intervals	Medium	Array, Sorting
0252	Meeting RoomsPremium	Easy	Array, Sorting
0242	Valid Anagram	Easy	Hash Table, String, Sorting
0049	Group Anagrams	Medium	Array, Hash Table, String +1

Prefix Sum (2)

Prefix Sum
No.	Problem	Difficulty	Topics
0238	Product of Array Except Self	Medium	Array, Prefix Sum
0253	Meeting Rooms IIPremium	Medium	Greedy, Array, Two Pointers +3

Binary Search (3)

Binary Search
No.	Problem	Difficulty	Topics
0153	Find Minimum in Rotated Sorted Array	Medium	Array, Binary Search
0033	Search in Rotated Sorted Array	Medium	Array, Binary Search
0300	Longest Increasing Subsequence	Medium	Array, Binary Search, Dynamic Programming

Two Pointers (5)

Two Pointers
No.	Problem	Difficulty	Topics
0015	3Sum	Medium	Array, Two Pointers, Sorting
0011	Container With Most Water	Medium	Greedy, Array, Two Pointers
0125	Valid Palindrome	Easy	Two Pointers, String
0005	Longest Palindromic Substring	Medium	Two Pointers, String, Dynamic Programming
0647	Palindromic Substrings	Medium	Two Pointers, String, Dynamic Programming

Bit Manipulation (5)

Bit Manipulation
No.	Problem	Difficulty	Topics
0371	Sum of Two Integers	Medium	Bit Manipulation, Math
0191	Number of 1 Bits	Easy	Bit Manipulation, Divide and Conquer
0338	Counting Bits	Easy	Bit Manipulation, Dynamic Programming
0268	Missing Number	Easy	Bit Manipulation, Array, Hash Table +3
0190	Reverse Bits	Easy	Bit Manipulation, Divide and Conquer

Breadth-First Search (2)

Breadth-First Search
No.	Problem	Difficulty	Topics
0322	Coin Change	Medium	Breadth-First Search, Array, Dynamic Programming
0133	Clone Graph	Medium	Depth-First Search, Breadth-First Search, Graph +1

Trie (4)

Trie
No.	Problem	Difficulty	Topics
0139	Word Break	Medium	Trie, Memoization, Array +3
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

Greedy (2)

Greedy
No.	Problem	Difficulty	Topics
0055	Jump Game	Medium	Greedy, Array, Dynamic Programming
0435	Non-overlapping Intervals	Medium	Greedy, Array, Dynamic Programming +1

Topological Sort (2)

Topological Sort
No.	Problem	Difficulty	Topics
0207	Course Schedule	Medium	Depth-First Search, Breadth-First Search, Graph +1
0269	Alien DictionaryPremium	Hard	Depth-First Search, Breadth-First Search, Graph +3

Matrix and Grid (4)

Matrix and Grid
No.	Problem	Difficulty	Topics
0417	Pacific Atlantic Water Flow	Medium	Depth-First Search, Breadth-First Search, Array +1
0073	Set Matrix Zeroes	Medium	Array, Hash Table, Matrix
0054	Spiral Matrix	Medium	Array, Matrix, Simulation
0048	Rotate Image	Medium	Array, Math, Matrix

Union-Find (4)

Union-Find
No.	Problem	Difficulty	Topics
0200	Number of Islands	Medium	Depth-First Search, Breadth-First Search, Union Find +2
0128	Longest Consecutive Sequence	Medium	Union Find, Array, Hash Table
0261	Graph Valid TreePremium	Medium	Depth-First Search, Breadth-First Search, Union Find +1
0323	Number of Connected Components in an Undirected GraphPremium	Medium	Depth-First Search, Breadth-First Search, Union Find +1

Other (2)

Other
No.	Problem	Difficulty	Topics
0057	Insert Interval	Medium	Array
0271	Encode and Decode StringsPremium	Medium	Design, Array, String

Linked List (6)

Linked List
No.	Problem	Difficulty	Topics
0206	Reverse Linked List	Easy	Recursion, Linked List
0141	Linked List Cycle	Easy	Hash Table, Linked List, Two Pointers
0021	Merge Two Sorted Lists	Easy	Recursion, Linked List
0023	Merge k Sorted Lists	Hard	Linked List, Divide and Conquer, Heap (Priority Queue) +1
0019	Remove Nth Node From End of List	Medium	Linked List, Two Pointers
0143	Reorder List	Medium	Stack, Recursion, Linked List +1

Backtracking (1)

Backtracking
No.	Problem	Difficulty	Topics
0079	Word Search	Medium	Depth-First Search, Array, String +2

Sliding Window (3)

Sliding Window
No.	Problem	Difficulty	Topics
0003	Longest Substring Without Repeating Characters	Medium	Hash Table, String, Sliding Window
0424	Longest Repeating Character Replacement	Medium	Hash Table, String, Sliding Window
0076	Minimum Window Substring	Hard	Hash Table, String, Sliding Window

Stack (1)

Stack
No.	Problem	Difficulty	Topics
0020	Valid Parentheses	Easy	Stack, String

Tree Traversal (11)

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
0124	Binary Tree Maximum Path Sum	Hard	Tree, Depth-First Search, Dynamic Programming +1
0102	Binary Tree Level Order Traversal	Medium	Tree, Breadth-First Search, Binary Tree
0297	Serialize and Deserialize Binary Tree	Hard	Tree, Depth-First Search, Breadth-First Search +3
0572	Subtree of Another Tree	Easy	Tree, Depth-First Search, Binary Tree +2
0105	Construct Binary Tree from Preorder and Inorder Traversal	Medium	Tree, Array, Hash Table +2
0098	Validate Binary Search Tree	Medium	Tree, Depth-First Search, Binary Search Tree +1
0230	Kth Smallest Element in a BST	Medium	Tree, Depth-First Search, Binary Search Tree +1
0235	Lowest Common Ancestor of a Binary Search Tree	Medium	Tree, Depth-First Search, Binary Search Tree +1

Heap / Priority Queue (2)

Heap / Priority Queue
No.	Problem	Difficulty	Topics
0347	Top K Frequent Elements	Medium	Array, Hash Table, Divide and Conquer +5
0295	Find Median from Data Stream	Hard	Design, Two Pointers, Data Stream +2

The Blind 75 is a published third-party selection, reproduced here by problem number in the order the list itself uses. 69 of its 75 entries carry a complete Python solution; the other 6 are LeetCode Premium (marked in the tables) or have no usable solution in our dataset, and are listed rather than dropped.

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The Blind 75 does not cover the problem you get asked.

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python

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

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.

Type your message...

GPT-6.1 Terra

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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...

GPT-6.1 TerraClear chat

Primary display

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

01Hash Map (1)1

02Dynamic Programming (10)10

03Sorting (5)5

04Prefix Sum (2)2

05Binary Search (3)3

06Two Pointers (5)5

07Bit Manipulation (5)5

08Breadth-First Search (2)2

09Trie (4)4

10Greedy (2)2

11Topological Sort (2)2

12Matrix and Grid (4)4

13Union-Find (4)4

14Other (2)2

15Linked List (6)6

16Backtracking (1)1

17Sliding Window (3)3

18Stack (1)1

19Tree Traversal (11)11

20Heap / Priority Queue (2)2

The Blind 75 does not cover the problem you get asked.

Approach

Approach

Approach

Other study lists

Hash Map (1)

Dynamic Programming (10)

Sorting (5)

Prefix Sum (2)

Binary Search (3)

Two Pointers (5)

Bit Manipulation (5)

Breadth-First Search (2)

Trie (4)

Greedy (2)

Topological Sort (2)

Matrix and Grid (4)

Union-Find (4)

Other (2)

Linked List (6)

Backtracking (1)

Sliding Window (3)

Stack (1)

Tree Traversal (11)

Heap / Priority Queue (2)