Algorithms

Data structures and algorithms for interviews and beyond: patterns, proofs, and practice problems.

23 of 103 problems solved · 22%

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01
Big-O & Recurrences
Asymptotic notation, recurrences, and the Master Theorem.
5/5 problems
- 1.1
  Big-O & Recurrences: growth rates, the Master Theorem, and three warm-ups
  Asymptotic notation, how to solve divide-and-conquer recurrences with the Master Theorem, and Pow(x, n), Sqrt(x), and merge sort, each from brute force to optimal with time and space complexity.
  Jul 24, 2025
Problems
- Read: Growth of Functions (Big-O, Big-Theta, Big-Omega)Medium
- Practice: Master Theorem and recurrencesMedium
- 50. Pow(x, n)Medium
- 69. Sqrt(x)Easy
- Self-assigned: implement Merge Sort and write recurrence solutionMedium
02
Arrays & Strings
Core operations, indexing, and common problems.
12/12 problems
- 2.1
  Arrays & Strings: 12 problems from brute force to optimal
  Hash maps, prefix products, in-place writes, reversal tricks, and sliding windows: twelve array and string problems, each solved three ways with time and space complexity.
  Jul 21, 2025
Problems
- 1. Two SumEasy
- 125. Valid PalindromeEasy
- 242. Valid AnagramEasy
- 121. Best Time to Buy and Sell StockEasy
- 238. Product of Array Except SelfMedium
- 27. Remove ElementEasy
- 283. Move ZeroesEasy
- 189. Rotate ArrayEasy
- 344. Reverse StringEasy
- 14. Longest Common PrefixEasy
- 567. Permutation in StringMedium
- 3. Longest Substring Without Repeating CharactersMedium
03
Two Pointers
Opposite-end and slow/fast pointers, including linked lists.
6/8 problems
- 3.1
  Two Pointers: opposite ends and slow/fast, six problems
  Two pointers on sorted arrays and on linked lists: pair sums, 3Sum, middles, cycles, and intersections, each from brute force to optimal with time and space complexity.
  Aug 8, 2025
Problems
- 167. Two Sum II - Input array is sortedEasy
- 15. 3SumMedium
- 876. Middle of the Linked ListEasy
- 141. Linked List CycleEasy
- 142. Linked List Cycle IIMedium
- 160. Intersection of Two Linked ListsEasy
- 92. Reverse Linked List IIMedium
- 11. Container With Most WaterMedium
04
Sliding Window
Fixed and variable windows, min/max windows, minimum window substring.
0/6 problems
Problems
05
Binary Search
Index search, binary search on the answer, rotated arrays, invariants.
0/8 problems
Problems
- 704. Binary SearchEasy
- 33. Search in Rotated Sorted ArrayMedium
- 34. Find First and Last Position of Element in Sorted ArrayMedium
- 153. Find Minimum in Rotated Sorted ArrayMedium
- 154. Find Minimum in Rotated Sorted Array IIMedium
- 278. First Bad VersionEasy
- 69. Sqrt(x)Easy
- 162. Find Peak ElementMedium
06
Divide & Conquer
Merge sort, quicksort, quickselect, and recurrence reasoning.
0/6 problems
Problems
- Read & Exercises: Divide-and-conquer techniques (merge sort, recurrences)Medium
- 912. Sort an Array (implement merge/quick as required)Medium
- 215. Kth Largest Element in an Array (quickselect)Medium
- 169. Majority Element (divide-and-conquer approach)Easy
- 493. Reverse Pairs (merge-sort/counting inversions variant)Hard
- 327. Count of Range Sum (divide-and-conquer advanced)Hard
07
Recursion & Backtracking
Tree recursion, permutations, combinations, and pruning.
0/10 problems
Problems
- 46. PermutationsMedium
- 47. Permutations IIMedium
- 78. SubsetsEasy
- 79. Word SearchMedium
- 22. Generate ParenthesesMedium
- 131. Palindrome PartitioningMedium
- 39. Combination SumMedium
- 40. Combination Sum IIMedium
- 17. Letter Combinations of a Phone NumberMedium
- 51. N-QueensHard
08
Greedy
Interval scheduling, sort-by-key heuristics, and exchange arguments.
0/6 problems
Problems
- 435. Non-overlapping IntervalsMedium
- 452. Minimum Number of Arrows to Burst BalloonsMedium
- 455. Assign CookiesEasy
- 55. Jump Game (greedy solution)Medium
- 45. Jump Game IIMedium
- Read & Exercises: Greedy algorithm design and proofsMedium
09
Dynamic Programming
1D/2D DP, memoization vs. tabulation, classic problems.
0/14 problems
Problems
- 70. Climbing StairsEasy
- 509. Fibonacci Number (memoization practice)Easy
- 198. House RobberMedium
- 213. House Robber IIMedium
- 300. Longest Increasing SubsequenceHard
- 53. Maximum Subarray (Kadane)Easy
- 322. Coin ChangeMedium
- 518. Coin Change 2Medium
- 139. Word BreakMedium
- 120. TriangleMedium
- 746. Min Cost Climbing StairsEasy
- 62. Unique PathsMedium
- Self-assigned: implement patience sorting for LISHard
- Read & Exercises: Dynamic Programming chapter (matrix-chain, optimal substructure)Hard
10
Graphs
BFS/DFS, shortest paths, topological sort, union-find.
0/10 problems
Problems
- 200. Number of IslandsMedium
- 133. Clone GraphMedium
- 207. Course ScheduleMedium
- 210. Course Schedule IIMedium
- 127. Word LadderHard
- 785. Is Graph Bipartite?Medium
- 261. Graph Valid TreeMedium
- 547. Number of Provinces (Union-Find)Medium
- 310. Minimum Height TreesMedium
- 1192. Critical Connections in a NetworkHard
11
Advanced Data Structures
Segment trees, Fenwick trees, tries, rolling hashes, bitmasks.
0/6 problems
Problems
- 307. Range Sum Query - Mutable (Segment Tree / BIT practice)Hard
- 208. Implement Trie (Prefix Tree)Medium
- 211. Add and Search Word - Data structure design (Trie + wildcard)Medium
- 315. Count of Smaller Numbers After Self (Fenwick / BIT or merge-sort)Hard
- Self-assigned: implement Fenwick Tree and Segment Tree (read+implement)Hard
- 28. Implement strStr() (practice rolling-hash/KMP ideas)Easy
12
Revision & Mock Interviews
Timed mixed sets, review of weak topics, mock interviews.
0/12 problems
Problems
- Top 50 Mediums (sample) - Mock set 1M/H
- Top 50 Mediums - Mock set 2M/H
- 23. Merge k Sorted ListsHard
- 297. Serialize and Deserialize Binary TreeHard
- 218. The Skyline ProblemHard
- 127. Word Ladder (review)Medium
- Self-assigned: pick 8 medium problems from earlier topics (timed)Medium
- LeetCode Mock Interview toolM/H
- 2-3 mock interviews (peer)M/H
- Do 3 timed 90-minute sessions covering mixed topicsHard
- Review: re-solve 10 previously failed problemsM/H
- LeetCode Explore / Top Interview Questions listMedium