LeetCode

Notes

• Stack
• Queue
• Trees and Graphs

Common Algorithms

Greatest common divisor (GCD) ⭑

• GCD of more than two (or array) numbers

BFS ⭑⭑

• 94: Binary Tree Inorder Traversal
• 102: Binary Tree Level Order Traversal
• 107: Binary Tree Level Order Traversal II
• 285: Inorder Successor in BST

DFS ⭑⭑

Binary Search ⭑⭑

• 35: Search Insert Position

Sliding Window ⭑⭑⭑⭑

• 159: Longest Substring with At Most Two Distinct Characters
• 340: Longest Substring with At Most K Distinct Characters

Common Algorithmic Paradigms

• Divide and Conquer
• Greedy Algorithm
• Backtracking
• Dynamic Programming

Algorithms

• Bit Manipulation
• Array and String
• Linked List
• Trees and Graphs
• Math

Divide and Conquer

#	Title	Solution	Difficulty
53	Maximum Subarray	Python	Easy
106	Construct Binary Tree from Inorder and Postorder Traversal	Python	Medium ⭑
169	Majority Element	Python	Easy

Greedy Algorithm

#	Title	Solution	Difficulty
402	Remove K Digits	Python	Medium
122	Best Time to Buy and Sell Stock II	Python	Easy

Backtracking

#	Title	Solution	Difficulty

Dynamic Programming

#	Title	Solution	Difficulty
53	Maximum Subarray	Python	Easy ⭑⭑⭑⭑
70	Climbing Stairs	Python	Easy ⭑⭑⭑
62	Unique Paths	Python	Medium ⭑⭑⭑⭑
91	Decode Ways	Python	Medium ⭑⭑⭑⭑
139	Word Break	Python	Medium 👾
121	Best Time to Buy and Sell Stock	Python	Easy
198	House Robber	Python	Easy

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Bit Manipulation

#	Title	Solution	Difficulty
231	Power of Two	Python	Easy
136	Single Number	Python	Easy

Array and String

#	Title	Solution	Difficulty
1	Two Sum	Swift	Easy
125	Valid Palindrome	Java, Python	Easy
20	Valid Parentheses	Python	Easy
929	Unique Email Addresses	Python	Easy
387	First Unique Character in a String	Python	Easy
66	Plus One	Python	Easy
686	Repeated String Match	Python	Easy
683	K Empty Slots	Python	Hard ⭑⭑⭑⭑
54	Spiral Matrix	Python	Medium ⭑
58	Length of Last Word	Python	Easy
42	Trapping Rain Water	Python	Hard ⭑⭑
159	Longest Substring with At Most Two Distinct Characters	Python	Hard ⭑⭑
340	Longest Substring with At Most K Distinct Characters	Python	Hard ⭑⭑⭑⭑
616	Add Bold Tag in String	Python	Medium
289	Game of Life	Python	Medium
349	Intersection of Two Arrays	Python	Easy
482	License Key Formatting	Python	Easy
169	Majority Element	Python	Easy ⭑⭑⭑
283	Move Zeroes	Python, Swift	Easy
448	Find All Numbers Disappeared in an Array	Python, Swift	Easy
581	Shortest Unsorted Continuous Subarray	Python	Easy
344	Reverse String	Python	Easy
14	Longest Common Prefix	Python	Easy
26	Remove Duplicates from Sorted Array	Python, Swift	Easy
27	Remove Element	Python, Swift	Easy
28	Implement strStr()	Python	Easy
35	Search Insert Position	Python	Easy
11	Container With Most Water	Python	Medium
88	Merge Sorted Array	Python	Easy
1081	Smallest Subsequence of Distinct Characters	Python	Medium 👾
485	Max Consecutive Ones	Swift	Easy
1295	Find Numbers with Even Number of Digits	Swift	Easy
977	Squares of a Sorted Array	Swift	Easy
1089	Duplicate Zeros	Swift	Easy
88	Merge Sorted Array	Swift	Easy
1346	Check If N and Its Double Exist	Python, Swift	Easy
941	Valid Mountain Array	Swift	Easy
1299	Replace Elements with Greatest Element on Right Side	Swift	Easy
905	Sort Array By Parity	Python, Swift	Easy
414	Third Maximum Number	Swift	Easy
1051	Height Checker	Swift	Easy

Linked List

#	Title	Solution	Difficulty
19	Remove Nth Node From End of List	Java	Medium
21	Merge Two Sorted Lists	Java, Python	Easy
83	Remove Duplicates from Sorted List	Java	Easy
86	Partition List	Java	Medium
92	Reverse Linked List II	Java	Medium
141	Linked List Cycle	Java	Easy
142	Linked List Cycle II	Java	Medium
160	Intersection of Two Linked Lists	Java	Easy
206	Reverse Linked List	Java	Easy
234	Palindrome Linked List	Java	Easy
237	Delete Node in a Linked List	Java	Easy
23	Merge k Sorted Lists	Python	Hard
708	Insert into a Cyclic Sorted List	👾	Medium
146	LRU Cache	Python	Medium

Trees and Graphs

#	Title	Solution	Difficulty
94	Binary Tree Inorder Traversal	Python, Swift	Easy
144	Binary Tree Preorder Traversal	Python, Swift	Easy
145	Binary Tree Postorder Traversal	Python, Swift	Easy
102	Binary Tree Level Order Traversal	Python, Swift	Medium
107	Binary Tree Level Order Traversal II	Python	Easy
104	Maximum Depth of Binary Tree	Python, Swift	Easy
101	Symmetric Tree	Python, Swift	Easy
112	Path Sum	Python, Swift	Easy
285	Inorder Successor in BST	Python	Medium ⭑⭑⭑⭑
98	Validate Binary Search Tree	Python	Medium ⭑⭑⭑⭑
105	Construct Binary Tree from Preorder and Inorder Traversal	Python	Medium ⭑
106	Construct Binary Tree from Inorder and Postorder Traversal	Python	Medium ⭑
889	Construct Binary Tree from Preorder and Postorder Traversal	Python	Medium ⭑⭑
235	Lowest Common Ancestor of a Binary Search Tree	Python	Easy ⭑
236	Lowest Common Ancestor of a Binary Tree	Python	Medium 👾
617	Merge Two Binary Trees	Python	Easy
687	Longest Univalue Path	Python	Easy
111	Minimum Depth of Binary Tree	Python	Easy
226	Invert Binary Tree	Python, Swift	Easy ⭑⭑⭑⭑
437	Path Sum III	Python	Easy 👾
538	Convert BST to Greater Tree	Python	Easy ⭑⭑⭑⭑
543	Diameter of Binary Tree	Python	Easy ⭑⭑⭑⭑
116	Populating Next Right Pointers in Each Node	Swift	Medium

Math

#	Title	Solution	Difficulty
7	Reverse Integer	Python	Easy
326	Power of Three	Python	Easy
412	Fizz Buzz	Python	Easy
136	Single Number	Python	Easy
13	Roman to Integer	Python	Easy
9	Palindrome Number	Python	Easy