Data Structures & Algorithms (DSA)

Curated solutions to LeetCode problems, algorithm design patterns, and computer science lab assignments.

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📊 Daily LeetCode & Problem Solving Tracker

#	Problem	Topic	Difficulty	Solution	Time	Space	Date Added
0001	Two Sum	Arrays & Hashing	Easy	Python	$O(n)$	$O(n)$	2026-09-08
0217	Contains Duplicate	Arrays & Hashing	Easy	Python	$O(n)$	$O(n)$	2026-09-09
0242	Valid Anagram	Arrays & Hashing	Easy	Python	$O(n)$	$O(1)$	2026-09-10
0049	Group Anagrams	Arrays & Hashing	Medium	Python	$O(N \cdot K)$	$O(N \cdot K)$	2026-09-11
0347	Top K Frequent Elements	Arrays & Hashing	Medium	Python	$O(n)$	$O(n)$	2026-09-12
0238	Product of Array Except Self	Arrays & Hashing	Medium	Python	$O(n)$	$O(1)$	2026-09-12
0036	Valid Sudoku	Arrays & Hashing	Medium	Python	$O(1)$	$O(1)$	2026-09-13
0128	Longest Consecutive Sequence	Arrays & Hashing	Medium	Python	$O(n)$	$O(n)$	2026-09-13
0125	Valid Palindrome	Two Pointers	Easy	Python	$O(n)$	$O(1)$	2026-09-15
0167	Two Sum II - Input Array Is Sorted	Two Pointers	Medium	Python	$O(n)$	$O(1)$	2026-09-15
0011	Container With Most Water	Two Pointers	Medium	Python	$O(n)$	$O(1)$	2026-09-17
0015	3Sum	Two Pointers	Medium	Python	$O(n^2)$	$O(1)$	2026-09-17
0042	Trapping Rain Water	Two Pointers	Hard	Python	$O(n)$	$O(1)$	2026-09-18
0121	Best Time to Buy and Sell Stock	Sliding Window	Easy	Python	$O(n)$	$O(1)$	2026-09-18
0003	Longest Substring Without Repeating Characters	Sliding Window	Medium	Python	$O(n)$	$O(min(m, n))$	2026-09-19
0424	Longest Repeating Character Replacement	Sliding Window	Medium	Python	$O(n)$	$O(1)$	2026-09-19
0567	Permutation in String	Sliding Window	Medium	Python	$O(n)$	$O(1)$	2026-09-19
0076	Minimum Window Substring	Sliding Window	Hard	Python	$O(m + n)$	$O(1)$	2026-09-19
0239	Sliding Window Maximum	Sliding Window	Hard	Python	$O(n)$	$O(k)$	2026-09-19
0020	Valid Parentheses	Stack	Easy	Python	$O(n)$	$O(n)$	2026-09-20
0155	Min Stack	Stack	Medium	Python	$O(1)$	$O(n)$	2026-09-20
0150	Evaluate Reverse Polish Notation	Stack	Medium	Python	$O(n)$	$O(n)$	2026-09-20
0022	Generate Parentheses	Stack	Medium	Python	$O(\frac{4^n}{\sqrt{n}})$	$O(n)$	2026-09-21
0739	Daily Temperatures	Stack	Medium	Python	$O(n)$	$O(n)$	2026-09-21
0853	Car Fleet	Stack	Medium	Python	$O(n \log n)$	$O(n)$	2026-09-22
0084	Largest Rectangle in Histogram	Stack	Hard	Python	$O(n)$	$O(n)$	2026-09-22
0704	Binary Search	Binary Search	Easy	Python	$O(\log n)$	$O(1)$	2026-09-23
0074	Search a 2D Matrix	Binary Search	Medium	Python	$O(\log(m \cdot n))$	$O(1)$	2026-09-23
0875	Koko Eating Bananas	Binary Search	Medium	Python	$O(n \cdot \log(\max(P)))$	$O(1)$	2026-09-23
0153	Find Minimum in Rotated Sorted Array	Binary Search	Medium	Python	$O(\log n)$	$O(1)$	2026-09-24
0033	Search in Rotated Sorted Array	Binary Search	Medium	Python	$O(\log n)$	$O(1)$	2026-09-24
0981	Time Based Key-Value Store	Binary Search	Medium	Python	$O(1)$ set / $O(\log m)$ get	$O(n)$	2026-09-24
0004	Median of Two Sorted Arrays	Binary Search	Hard	Python	$O(\log(\min(m, n)))$	$O(1)$	2026-09-25
0206	Reverse Linked List	Linked List	Easy	Python	$O(n)$	$O(1)$	2026-09-25
0021	Merge Two Sorted Lists	Linked List	Easy	Python	$O(n + m)$	$O(1)$	2026-09-25
0143	Reorder List	Linked List	Medium	Python	$O(n)$	$O(1)$	2026-09-26
0019	Remove Nth Node From End of List	Linked List	Medium	Python	$O(n)$	$O(1)$	2026-09-26
0138	Copy List with Random Pointer	Linked List	Medium	Python	$O(n)$	$O(1)$	2026-09-26

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📚 Lab Assignments

• Lab 1 — Library Borrowing Frequency & Counter Analytics
• Lab 2 — Array Operations & Search Procedures
• Lab 3 — Stack Implementation & Expression Evaluation
• Lab 4 — Queue Architectures & Buffer Management
• Lab 5 — Linked List Manipulation & Traversal
• Lab 6 — Binary Search Trees (BST) & In-order Walk
• Lab 8 — Graph Representation & Traversal (BFS/DFS)

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🛠️ How to Run Tests

Run individual problem solutions directly with Python:

python leetcode/0001_two_sum.py

Or execute all tests using pytest:

pytest leetcode/