winstontsui / leetcode-problems

Sample solutions for coding interview problems from LeetCode, in Java.

Leetcode-problems by Winston Tsui

Link to Google Spreadsheet

Notes

API tutorial from freeCodeCamp.org Currently 41 minutes in

MIT Missing Semester in CS Education Currently on Lecture 1, 16 minutes in

Get All GitHub Badges

Check remote repository I'm pushing and pulling from: git remote -v

git config --global user.name git config --global user.email KeyChain Access

git status shows information about files in my directory since the last commit.

Questions or comments? Contact me at [e-mail]

Reference to ReadMe Documentation

Solved LeetCode Problems

Date	#	Name	Topics	Difficulty	Link
8/25/24	61	Rotate List	Linked List, Two Pointers	Medium	Here
8/12/24	513	Find Bottom Left Tree Value	Tree, BFS	Medium	Here
8/6/24	535	Encode and Decode TinyURL	Hash Table, String, Design	Medium	Here
8/5/24	2405	Optimal Partition of String	Hash Table, String, Greedy	Medium	Here
7/26/24	901	Online Stock Span	Monotonic Stack, Data Stream	Medium	Here
7/18/24	2971	Find Polygon With the Largest Perimeter	Array, Sorting, Prefix Sum	Medium	Here
7/18/24	752	Open the Lock	Array, Hash Table, String, BFS	Medium	Here
7/16/24	96	Unique Binary Search Trees	Math, Dynamic Programming, Tree	Medium	Here
7/15/24	2652	Sum Multiples	Math	Easy	Here
7/14/24	1672	Richest Customer Wealth	Array	Easy	Here
7/12/24	1207	Unique Number of Occurrences	Array, Hash Table	Easy	Here
7/12/24	1466	Reorder Routes to Make All Paths Lead to the City Zero	DFS, Graph	Medium	Here
7/7/24	904	Fruit Into Baskets	Array, Hash Table, Sliding Window	Medium	Here
7/5/24	1838	Frequency of the Most Frequent Element	Sliding Window, Sorting, Prefix Sum	Medium	Here
7/2/24	83	Remove Duplicates from Sorted List	Linked List	Easy	Here
7/1/24	24	Swap Nodes in Pairs	Linked List, Recursion	Medium	Here
6/30/24	359	Logger Rate Limiter	Hash Table, Design, Data Stream	Easy	Here
6/30/24	286	Walls and Gates	Array, BFS, Matrix	Medium	Here
6/29/24	146	LRU Cache	Hash Table, Design, Doubly-Linked List	Medium	Here
6/28/24	280	Wiggle Sort	Array, Greedy, Sorting	Medium	Here
6/28/24	229	Majority Element II	Array, Hash Table, Counting	Medium	Here
6/26/24	234	Palindrome Linked List	Linked List, Two Pointers	Easy	Here
6/25/24	740	Delete and Earn	Array, Dynamic Programming	Medium	Here
6/25/24	472	Concatenated Words	Array, String, Dynamic Programming	Hard	Here
6/22/24	21	Merge Two Sorted Lists	Linked List, Recursion	Easy	Here
6/21/24	496	Next Greater Element I	Array, Hash Table, Monotonic Stack	Easy	Here
6/18/24	383	Ransom Note	Hash Table, String	Easy	Here
6/18/24	232	Implement Queue using Stacks	Stack, Design, Queue	Easy	Here
6/17/24	1046	Last Stone Weight	Array, Heap (Priority Queue)	Easy	Here
6/17/24	33	Search in Rotated Sorted Array	Array, Binary Search	Medium	Here
6/15/24	933	Number of Recent Calls	Design, Queue, Data Stream	Easy	Here
6/15/24	703	Kth Largest Element in a Stream	Tree, Design, Heap	Easy	Here
6/14/24	13	Roman to Integer	Hash Table, Math, String	Easy	Here
6/14/24	355	Design Twitter	Hash Table, Design, Heap	Medium	Here
6/12/24	1436	Destination City	Array, HashSet, String	Easy	Here
6/11/24	373	Find K Pairs with Smallest Sums	Array, Heap (Priority Queue)	Medium	Here
6/10/24	567	Permutation in String	Hash, String, Sliding Window	Medium	Here
6/10/24	853	Car Fleet	Array, Monotonic Stack, Sorting	Medium	Here
6/8/24	739	Daily Temperatures	Array, Stack	Medium	Here
6/6/24	155	Min Stack	Stack, Design	Medium	Here
6/5/24	1462	Course Schedule IV	DFS, BFS, Graph	Medium	Here
6/5/24	169	Majority Element	Array, Hash Table, Sorting	Easy	Here
6/3/24	75	Sort Colors	Array, Two Pointers, Sorting	Medium	Here
6/3/24	606	Construct String from Binary Tree	String, Tree, DFS	Medium	Here
6/2/24	50	Pow(x, n)	Math, Recursion	Medium	Here
5/29/24	909	Snakes and Ladders	Array, BFS, Matrix	Medium	Here
5/28/24	130	Surrounded Regions	Array, DFS, Matrix	Medium	Here
5/27/24	743	Encode and Decode Strings	BFS, Graph, Heap	Medium	Here
5/22/24	271	Encode and Decode Strings	Array, String	Medium	Here
5/22/24	199	Binary Tree Right Side View	Tree, Depth-First Search	Medium	Here
5/14/24	344	Reverse String	Two Pointers, String	Easy	Here
5/3/24	1448	Count Good Nodes in Binary Tree	Tree, Depth-First Search	Medium	Here
5/1/24	105	Construct Binary Tree from Preorder and Inorder Traversal	Array, Tree	Medium	Here
4/20/24	704	Binary Search	Array, Binary Search	Easy	Here
4/16/24	48	Rotate Image	Array, Math, Matrix	Medium	Here
4/13/24	994	Rotting Oranges	Array, BFS, Matrix	Medium	Here
4/12/24	139	Word Break	Array, DP, Memoization	Medium	Here
4/10/24	2331	Evaluate Boolean Binary Tree	Tree, Depth-First Search	Easy	Here
4/10/24	404	Sum of Left Leaves	Tree, Depth-First Search	Easy	Here
4/9/24	113	Path Sum II	Backtracking, Tree, DFS	Medium	Here
4/7/24	53	Maximum Subarray	Array, Two Pointers	Medium	Here
4/6/24	236	Lowest Common Ancestor of a Binary Tree	Tree, Depth-First Search	Medium	Here
4/4/24	129	Sum Root to Leaf Numbers	Tree, Depth-First Search	Medium	Here
4/4/24	543	Diameter of Binary Tree	Tree, Depth-First Search	Easy	Here
4/2/24	213	House Robber II	Array, Dynamic Programming	Medium	Here
4/1/24	198	House Robber	Array, Dynamic Programming	Medium	Here
3/30/24	322	Coin Change	Array, Dynamic Programming	Medium	Here
3/28/24	110	Balanced Binary Tree	Tree, Depth-First Search	Easy	Here
3/26/24	101	Symmetric Tree	Tree, Depth-First Search	Easy	Here
3/26/24	347	Top K Frequent Elements	Array, Hash Table, Heap	Medium	Here
3/23/24	22	Generate Parentheses	Backtracking, Stack	Medium	Here
3/21/24	1047	Remove All Adjacent Duplicates In String	String, Stack	Easy	Here
3/19/24	153	Find Minimum in Rotated Sorted Array	Array, Binary Search	Medium	Here
3/18/24	141	Linked List Cycle	Linked List, Two Pointers	Easy	Here
3/16/24	268	Missing Number	Array, Bit Manipulation	Easy	Here
3/14/24	190	Reverse Bits	Bit Manipulation	Easy	Here
3/12/24	216	Graph Valid Tree	Graph, Depth-First Search	Medium	Here
3/11/24	338	Counting Bits	Dynamic Programming, Bit Manipulation	Easy	Here
3/10/24	191	Number of 1 Bits	Bit Manipulation	Easy	Here
3/9/24	323	Number of Connected Components in an Undirected Graph	Depth-First Search, Breadth-First Search	Medium	Here
3/7/24	1021	Remove Outermost Parentheses	String, Stack	Easy	Here
3/6/24	2	Add Two Numbers	Math, Linked List	Medium	Here
3/5/24	207	Course Schedule	Depth-First Search, Graph	Medium	Here
3/5/24	20	Valid Parentheses	String, Stack	Easy	Here
3/5/24	150	Evaluate Reverse Polish Notation	Array, Math, Stack	Medium	Here
3/4/24	217	Contains Duplicate	Array, Hash Table	Easy	Here
3/2/24	62	Unique Paths	Dynamic Programming, Math	Medium	Here
3/2/24	15	3Sum	Array, Two Pointers, Sorting	Medium	Here
2/27/24	230	Kth Smallest Element in a BST	Binary Tree, Inorder Traversal	Medium	Here
2/27/24	88	Merge Sorted Array	Array, Three Pointers	Medium	Here
2/27/24	98	Binary Tree Level Order Traversal II	Depth-First Search, Binary Tree	Medium	Here
2/26/24	78	Subsets	Array, Backtracking	Medium	Here
2/25/24	107	Binary Tree Level Order Traversal II	Tree, Breadth-First Search	Medium	Here
2/25/24	102	Binary Tree Level Order Traversal	Tree, Breadth-First Search	Medium	Here
2/25/24	235	Lowest Common Ancestor of a Binary Search Tree	Tree, Binary Search Tree, DFS	Medium	Here
2/24/24	104	Maximum Depth of Binary Tree	Tree, DFS	Easy	Here
2/23/24	572	Subtree of Another Tree	Tree, DFS	Easy	Here
2/23/24	100	Same Tree	Tree, DFS	Easy	Here
2/23/24	1	Two Sum	Array, Hash Table	Easy	Here
2/17/24	200	Number of Islands	Graph, DFS, BFS	Medium	Here
2/17/24	133	Clone Graph	Graph, DFS	Medium	Here
2/15/24	223	Rectangle Area	Math, Geometry	Medium	Here
2/14/24	143	Reorder List	Linked List, Two Pointers	Medium	Here
2/13/24	70	Climbing Stairs	Dynamic Programming	Easy	Here
2/12/24	238	Product of Array Except Self	Array, Prefix Sum	Medium	Here
2/10/24	226	Invert Binary Tree	Tree, Recursion	Easy	Here
2/10/24	206	Reverse Linked List	Linked List, Iteration	Easy	Here
2/8/24	49	Group Anagrams	String, Hash Table	Medium	Here
2/8/24	417	Pacific Atlantic Water Flow	DFS, BFS	Medium	Here
2/3/24	424	Longest Repeating Character Replacement	Two Pointers, Sliding Window	Medium	Here
1/26/24	11	Container With Most Water	Array, Two Pointers	Medium	Here
1/9/24	19	Remove Nth Node From End of List	Linked List, Two Pointers	Medium	Here
1/9/24	876	Middle of the Linked List	Linked List, Tortoise and Hare	Easy	Here
1/9/24	3	Longest Substring Without Repeating Characters	Two Pointers, Sliding Window	Medium	Here
1/7/24	128	Longest Consecutive Sequence	Array, Union Find	Medium	Here
1/7/24	237	Delete Node in a Linked List	Linked List	Medium	Here
1/6/24	2870	Minimum Number of Operations to Make Array Empty	Math, Simulation	Medium	Here
1/6/24	18	4Sum	Array, Two Pointers	Medium	Here
1/3/24	74	Search a 2D Matrix	Binary Search	Medium	Here
1/3/24	31	Next Permutation	Array, Next Permutation	Medium	Here
1/1/24	118	Pascal's Triangle	Array	Easy	Here
1/1/24	73	Set Matrix Zeroes	Array	Medium	Here

Written Notes

Leetcode 61

Leetcode 83

Leetcode 24

Leetcode 146

Leetcode 567

Leetcode 853

Leetcode 1462

Leetcode 105 Construct Binary Tree from Preorder and Inorder Traversal

Leetcode 48 Rotate Image

Leetcode 22 Generate Parentheses

Leetcode 268 Missing Number

Leetcode 133 Clone Graph DFS Approach

Leetcode 1021 Remove Outermost Parentheses

Leetcode 100 Is Same Tree

Leetcode 78 Subsets

About me

My name is Winston Tsui! I'm a Computer Science student who loves coding and programming. I like to create, experiment and develop technical applications, and am generally passionate about using code and technology as part of digitally-based solutions to some of our biggest challenges in healthcare technology, media and finance.

I am experienced in multiple CS domains, including Graphics (C++, OpenGL), Data Analysis (Python, Scikit-learn), Virtual Reality (C#, Unity), Pervasive Computing (Android Studio, Kotlin), Operating Systems, Algorithms and Data Structures. In my free time, I have developed full stack e-commerce, portfolio and messaging applications using languages such as Dart and JavaScript and also frameworks such as daisyUI, React and Next.js. (Check out my open source code at https://github.com/winstontsui). I have experience deploying these applications on the Play Store and on the web using Netlify and Vercel. (Check out my website at https://melodic-capybara-ca9ddd.netlify.app/). My software engineering experience thoroughly encompasses multiple programming languages, frameworks and technologies, spanning from version control knowledge of Git and GitHub to SQL database design and MongoDB.

My research interest lies in full-stack software engineering incorporating machine learning (ML) predictive analytics features. Dr. Hoda Eldardity's work from Virginia Tech is a great example- addressing challenges in extracting new attribute-value pairs with limited labeled data through a multi-label learning framework. Her deep learning research using dynamic threshold learning for multi-label inference has shown significant improvement in unseen scenarios. I’m motivated by this research because scientific data extraction can drastically improve our current automated analysis of clinical diagnostics; this is something I want to explore.

I see myself utilizing my technical expertise in web development and Android development to create digital solutions to some of the our most pressing challenges, especially healthcare technology and ML predictive-analytics based work.

Hoping to become a software engineer one day🙏 Check out my projects: https://github.com/winstontsui

Follow me on LinkedIn!!

Contact me at [e-mail]