The LeetCode 75 Study Plan

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.

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Easy: 22
Medium: 53
Hard: 0
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.

Two Pointers (9)

Two Pointers
No.	Problem	Difficulty	Topics
1768	Merge Strings Alternately	Easy	Two Pointers, String
0345	Reverse Vowels of a String	Easy	Two Pointers, String
0151	Reverse Words in a String	Medium	Two Pointers, String
0443	String Compression	Medium	Two Pointers, String
0283	Move Zeroes	Easy	Array, Two Pointers
0392	Is Subsequence	Easy	Two Pointers, String, Dynamic Programming
0011	Container With Most Water	Medium	Greedy, Array, Two Pointers
1679	Max Number of K-Sum Pairs	Medium	Array, Hash Table, Two Pointers +1
2300	Successful Pairs of Spells and Potions	Medium	Array, Two Pointers, Binary Search +1

Math and Number Theory (1)

Math and Number Theory
No.	Problem	Difficulty	Topics
1071	Greatest Common Divisor of Strings	Easy	Math, String

Other (1)

Other
No.	Problem	Difficulty	Topics
1431	Kids With the Greatest Number of Candies	Easy	Array

Greedy (5)

Greedy
No.	Problem	Difficulty	Topics
0605	Can Place Flowers	Easy	Greedy, Array
0334	Increasing Triplet Subsequence	Medium	Greedy, Array
0714	Best Time to Buy and Sell Stock with Transaction Fee	Medium	Greedy, Array, Dynamic Programming
0435	Non-overlapping Intervals	Medium	Greedy, Array, Dynamic Programming +1
0452	Minimum Number of Arrows to Burst Balloons	Medium	Greedy, Array, Sorting

Prefix Sum (3)

Prefix Sum
No.	Problem	Difficulty	Topics
0238	Product of Array Except Self	Medium	Array, Prefix Sum
1732	Find the Highest Altitude	Easy	Array, Prefix Sum
0724	Find Pivot Index	Easy	Array, Prefix Sum

Sliding Window (4)

Sliding Window
No.	Problem	Difficulty	Topics
0643	Maximum Average Subarray I	Easy	Array, Sliding Window
1456	Maximum Number of Vowels in a Substring of Given Length	Medium	String, Sliding Window
1004	Max Consecutive Ones III	Medium	Array, Binary Search, Prefix Sum +1
1493	Longest Subarray of 1's After Deleting One Element	Medium	Array, Dynamic Programming, Sliding Window

Hash Map (2)

Hash Map
No.	Problem	Difficulty	Topics
2215	Find the Difference of Two Arrays	Easy	Array, Hash Table
1207	Unique Number of Occurrences	Easy	Array, Hash Table

Sorting (1)

Sorting
No.	Problem	Difficulty	Topics
1657	Determine if Two Strings Are Close	Medium	Hash Table, String, Counting +1

Matrix and Grid (3)

Matrix and Grid
No.	Problem	Difficulty	Topics
2352	Equal Row and Column Pairs	Medium	Array, Hash Table, Matrix +1
1926	Nearest Exit from Entrance in Maze	Medium	Breadth-First Search, Array, Matrix
0994	Rotting Oranges	Medium	Breadth-First Search, Array, Matrix

Stack (7)

Stack
No.	Problem	Difficulty	Topics
2390	Removing Stars From a String	Medium	Stack, String, Simulation
0735	Asteroid Collision	Medium	Stack, Array, Simulation
0394	Decode String	Medium	Stack, Recursion, String
0933	Number of Recent Calls	Easy	Design, Queue, Data Stream
0649	Dota2 Senate	Medium	Greedy, Queue, String
0739	Daily Temperatures	Medium	Stack, Array, Monotonic Stack
0901	Online Stock Span	Medium	Stack, Design, Data Stream +1

Linked List (4)

Linked List
No.	Problem	Difficulty	Topics
2095	Delete the Middle Node of a Linked List	Medium	Linked List, Two Pointers
0328	Odd Even Linked List	Medium	Linked List
0206	Reverse Linked List	Easy	Recursion, Linked List
2130	Maximum Twin Sum of a Linked List	Medium	Stack, Linked List, Two Pointers

Tree Traversal (10)

Tree Traversal
No.	Problem	Difficulty	Topics
0104	Maximum Depth of Binary Tree	Easy	Tree, Depth-First Search, Breadth-First Search +1
0872	Leaf-Similar Trees	Easy	Tree, Depth-First Search, Binary Tree
1448	Count Good Nodes in Binary Tree	Medium	Tree, Depth-First Search, Breadth-First Search +1
0437	Path Sum III	Medium	Tree, Depth-First Search, Binary Tree
1372	Longest ZigZag Path in a Binary Tree	Medium	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
1161	Maximum Level Sum of a Binary Tree	Medium	Tree, Depth-First Search, Breadth-First Search +1
0700	Search in a Binary Search Tree	Easy	Tree, Binary Search Tree, Binary Tree
0450	Delete Node in a BST	Medium	Tree, Binary Search Tree, Binary Tree

Breadth-First Search (2)

Breadth-First Search
No.	Problem	Difficulty	Topics
0841	Keys and Rooms	Medium	Depth-First Search, Breadth-First Search, Graph
1466	Reorder Routes to Make All Paths Lead to the City Zero	Medium	Depth-First Search, Breadth-First Search, Graph

Union-Find (2)

Union-Find
No.	Problem	Difficulty	Topics
0547	Number of Provinces	Medium	Depth-First Search, Breadth-First Search, Union Find +1
0399	Evaluate Division	Medium	Depth-First Search, Breadth-First Search, Union Find +4

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
2336	Smallest Number in Infinite Set	Medium	Design, Hash Table, Ordered Set +1
2542	Maximum Subsequence Score	Medium	Greedy, Array, Sorting +1
2462	Total Cost to Hire K Workers	Medium	Array, Two Pointers, Simulation +1

Binary Search (3)

Binary Search
No.	Problem	Difficulty	Topics
0374	Guess Number Higher or Lower	Easy	Binary Search, Interactive
0162	Find Peak Element	Medium	Array, Binary Search
0875	Koko Eating Bananas	Medium	Array, Binary Search

Backtracking (2)

Backtracking
No.	Problem	Difficulty	Topics
0017	Letter Combinations of a Phone Number	Medium	Hash Table, String, Backtracking
0216	Combination Sum III	Medium	Array, Backtracking

Dynamic Programming (7)

Dynamic Programming
No.	Problem	Difficulty	Topics
1137	N-th Tribonacci Number	Easy	Memoization, Math, Dynamic Programming
0746	Min Cost Climbing Stairs	Easy	Array, Dynamic Programming
0198	House Robber	Medium	Array, Dynamic Programming
0790	Domino and Tromino Tiling	Medium	Dynamic Programming
0062	Unique Paths	Medium	Math, Dynamic Programming, Combinatorics
1143	Longest Common Subsequence	Medium	String, Dynamic Programming
0072	Edit Distance	Medium	String, Dynamic Programming

Bit Manipulation (3)

Bit Manipulation
No.	Problem	Difficulty	Topics
0338	Counting Bits	Easy	Bit Manipulation, Dynamic Programming
0136	Single Number	Easy	Bit Manipulation, Array
1318	Minimum Flips to Make a OR b Equal to c	Medium	Bit Manipulation

Trie (2)

Trie
No.	Problem	Difficulty	Topics
0208	Implement Trie (Prefix Tree)	Medium	Design, Trie, Hash Table +1
1268	Search Suggestions System	Medium	Trie, Array, String +3

The LeetCode 75 is a published third-party selection, reproduced here by problem number in the order the list itself uses. 75 of its 75 entries carry a complete Python solution.

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The LeetCode 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

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

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

01Two Pointers (9)9

02Math and Number Theory (1)1

03Other (1)1

04Greedy (5)5

05Prefix Sum (3)3

06Sliding Window (4)4

07Hash Map (2)2

08Sorting (1)1

09Matrix and Grid (3)3

10Stack (7)7

11Linked List (4)4

12Tree Traversal (10)10

13Breadth-First Search (2)2

14Union-Find (2)2

15Heap / Priority Queue (4)4

16Binary Search (3)3

17Backtracking (2)2

18Dynamic Programming (7)7

19Bit Manipulation (3)3

20Trie (2)2

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

Approach

Approach

Approach

Other study lists

Two Pointers (9)

Math and Number Theory (1)

Other (1)

Greedy (5)

Prefix Sum (3)

Sliding Window (4)

Hash Map (2)

Sorting (1)

Matrix and Grid (3)

Stack (7)

Linked List (4)

Tree Traversal (10)

Breadth-First Search (2)

Union-Find (2)

Heap / Priority Queue (4)

Binary Search (3)

Backtracking (2)

Dynamic Programming (7)

Bit Manipulation (3)

Trie (2)