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🎯 DSA Master Learning Plan - Pattern by Pattern

#leetcode #dsa #algorithms #datastructures

📖 My Story

Like many developers, I've been putting off learning DSA for months. The truth? I don't have endless hours to dedicate, and honestly, the traditional "solve 1000 problems" approach felt overwhelming.

So I did something different - I used AI to build a custom learning plan that fits MY schedule and learning style. This isn't another generic DSA roadmap. This is a stress-free, pattern-focused approach that prioritizes depth over breadth.

Important: I'm posting this publicly before I even start. Why? Because having this here means it'll be waiting for me whenever I'm ready to begin. Maybe it'll help you too.

🎨 How I Built This Plan

I spent time with Claude AI to:

  1. Break down DSA into digestible patterns
  2. Order them from foundational to advanced
  3. Select 10-15 problems per pattern (not 100!)
  4. Build in revision cycles so I don't forget
  5. Make it flexible - no rigid daily schedules

The philosophy is simple: Master one pattern deeply before moving to the next.

My Philosophy: Master one pattern at a time. Solve 10+ problems per pattern before moving on.

Timeline: 1 year to become a DSA master (stress-free!)

Revision: Every fortnight, solve 2-3 problems from already mastered patterns

📚 Learning Order (Beginner → Advanced)

Phase 1: Foundation (Weeks 1-8)

Start here. These patterns build your fundamental problem-solving skills.

✅ Pattern 1: Array Basics

Goal: Understand array traversal, basic operations

Problems to Master: 10-12 problems

Core Concepts:

  • Index manipulation
  • In-place modifications
  • Frequency counting

Problem Set (Start with these):

  1. 217. Contains Duplicate - Easy warmup
  2. 169. Majority Element - Boyer-Moore voting
  3. 189. Rotate Array - Reversal technique
  4. 41. First Missing Positive - Index as hash
  5. 442. Find All Duplicates in an Array
  6. 448. Find All Numbers Disappeared in an Array
  7. 287. Find the Duplicate Number
  8. 243. Shortest Word Distance
  9. 849. Maximize Distance to Closest Person
  10. 384. Shuffle an Array - Fisher-Yates

C# Data Structures Used: int[], List<int>, HashSet<int>

✅ Pattern 2: Two Pointers - Same Direction

Goal: Learn to use two pointers moving in same direction

Problems to Master: 10-12 problems

Core Concepts:

  • Slow-fast pointer
  • Remove duplicates
  • In-place array modification

Problem Set:

  1. 283. Move Zeroes - Classic starter
  2. 27. Remove Element
  3. 26. Remove Duplicates from Sorted Array
  4. 80. Remove Duplicates from Sorted Array II
  5. 75. Sort Colors - Dutch National Flag
  6. 121. Best Time to Buy and Sell Stock
  7. 122. Best Time to Buy and Sell Stock II
  8. 31. Next Permutation
  9. 556. Next Greater Element III
  10. 165. Compare Version Numbers
  11. 1574. Shortest Subarray to be Removed to Make Array Sorted

C# Skills: Index manipulation, while loops with two indices

✅ Pattern 3: Two Pointers - Opposite Direction

Goal: Pointers moving from both ends toward center

Problems to Master: 10-12 problems

Core Concepts:

  • Left-right convergence
  • Palindrome checks
  • Two Sum variants

Problem Set:

  1. 125. Valid Palindrome - Start here
  2. 344. Reverse String
  3. 680. Valid Palindrome II
  4. 167. Two Sum II - Input Array Is Sorted
  5. 15. 3Sum - Important pattern
  6. 16. 3Sum Closest
  7. 18. 4Sum
  8. 977. Squares of a Sorted Array
  9. 11. Container With Most Water - Classic
  10. 42. Trapping Rain Water - Must master
  11. 5. Longest Palindromic Substring

Key Algorithm: Expand around center technique

✅ Pattern 4: Sliding Window - Fixed Size

Goal: Maintain a window of fixed size

Problems to Master: 6-8 problems

Core Concepts:

  • Add right, remove left
  • Running sum/count

Problem Set:

  1. 1100. Find K-Length Substrings With No Repeated Characters
  2. 1151. Minimum Swaps to Group All 1's Together
  3. 2134. Minimum Swaps to Group All 1's Together II
  4. 1423. Maximum Points You Can Obtain from Cards
  5. 187. Repeated DNA Sequences
  6. 346. Moving Average from Data Stream

C# Data Structures: Queue<int>, Dictionary<char, int>

✅ Pattern 5: Sliding Window - Variable Size

Goal: Shrink/expand window based on condition

Problems to Master: 10-12 problems

Core Concepts:

  • While loop to shrink window
  • Expand on every iteration
  • Track min/max window

Problem Set:

  1. 3. Longest Substring Without Repeating Characters - Must know
  2. 209. Minimum Size Subarray Sum
  3. 340. Longest Substring with At Most K Distinct Characters
  4. 904. Fruit Into Baskets
  5. 424. Longest Repeating Character Replacement
  6. 567. Permutation in String
  7. 438. Find All Anagrams in a String
  8. 76. Minimum Window Substring - Hard but essential
  9. 30. Substring with Concatenation of All Words
  10. 395. Longest Substring with At Least K Repeating Characters

This is THE most important pattern for interviews!

✅ Pattern 6: HashMap / HashSet

Goal: O(1) lookups for efficiency

Problems to Master: 12-15 problems

Core Concepts:

  • Frequency maps
  • Index storage
  • Set operations

Problem Set:

  1. 1. Two Sum - Classic starter
  2. 242. Valid Anagram
  3. 383. Ransom Note
  4. 387. First Unique Character in a String
  5. 49. Group Anagrams
  6. 128. Longest Consecutive Sequence
  7. 205. Isomorphic Strings
  8. 409. Longest Palindrome
  9. 953. Verifying an Alien Dictionary
  10. 380. Insert Delete GetRandom O(1)
  11. 1010. Pairs of Songs With Total Durations Divisible by 60
  12. 299. Bulls and Cows

C# Data Structures: Dictionary<TKey, TValue>, HashSet<T>

Phase 2: Intermediate Patterns (Weeks 9-20)

✅ Pattern 7: Prefix Sum

Goal: Precompute cumulative sums for range queries

Problems to Master: 10-12 problems

Core Concepts:

  • Running sum array
  • Range sum = prefix[j] - prefix[i-1]
  • HashMap for subarray sums

Problem Set:

  1. 303. Range Sum Query - Immutable - Start here
  2. 304. Range Sum Query 2D - Immutable
  3. 238. Product of Array Except Self
  4. 724. Find Pivot Index
  5. 560. Subarray Sum Equals K - Important
  6. 525. Contiguous Array
  7. 523. Continuous Subarray Sum
  8. 974. Subarray Sums Divisible by K
  9. 1248. Count Number of Nice Subarrays
  10. 1031. Maximum Sum of Two Non-Overlapping Subarrays

Key Technique: Use HashMap to store prefix sums

✅ Pattern 8: Stack / Queue

Goal: LIFO and FIFO operations

Problems to Master: 10-12 problems

Core Concepts:

  • Valid parentheses
  • Expression evaluation
  • Nested structures

Problem Set:

  1. 20. Valid Parentheses - Must know
  2. 155. Min Stack
  3. 150. Evaluate Reverse Polish Notation
  4. 224. Basic Calculator
  5. 227. Basic Calculator II
  6. 394. Decode String
  7. 71. Simplify Path
  8. 1249. Minimum Remove to Make Valid Parentheses
  9. 232. Implement Queue using Stacks
  10. 225. Implement Stack using Queues

C# Data Structures: Stack<T>, Queue<T>

✅ Pattern 9: Monotonic Stack/Queue

Goal: Maintain increasing/decreasing order

Problems to Master: 8-10 problems

Core Concepts:

  • Next greater/smaller element
  • Maintain stack invariant
  • O(n) solutions

Problem Set:

  1. 739. Daily Temperatures - Start here
  2. 496. Next Greater Element I
  3. 503. Next Greater Element II
  4. 402. Remove K Digits
  5. 239. Sliding Window Maximum - Classic
  6. 1438. Longest Continuous Subarray With Absolute Diff Less Than or Equal to Limit
  7. 862. Shortest Subarray with Sum at Least K

This pattern is a game-changer for optimization!

✅ Pattern 10: Binary Search

Goal: O(log n) search in sorted spaces

Problems to Master: 12-15 problems

Core Concepts:

  • Template: while (left <= right)
  • Binary search on answer
  • Rotated arrays

Problem Set:

  1. 704. Binary Search - Template
  2. 35. Search Insert Position
  3. 34. Find First and Last Position of Element in Sorted Array
  4. 74. Search a 2D Matrix
  5. 33. Search in Rotated Sorted Array
  6. 153. Find Minimum in Rotated Sorted Array
  7. 162. Find Peak Element
  8. 278. First Bad Version
  9. 875. Koko Eating Bananas - Binary search on answer
  10. 1011. Capacity To Ship Packages Within D Days
  11. 4. Median of Two Sorted Arrays - Hard
  12. 981. Time Based Key-Value Store

Learn the template pattern FIRST!

✅ Pattern 11: Intervals / Line Sweep

Goal: Merge, intersect, and manage intervals

Problems to Master: 10-12 problems

Core Concepts:

  • Sort by start time
  • Merge overlapping intervals
  • Event-based processing

Problem Set:

  1. 252. Meeting Rooms - Easy start
  2. 56. Merge Intervals - Must know
  3. 57. Insert Interval
  4. 435. Non-overlapping Intervals
  5. 986. Interval List Intersections
  6. 253. Meeting Rooms II - Use heap
  7. 452. Minimum Number of Arrows to Burst Balloons
  8. 1288. Remove Covered Intervals
  9. 1229. Meeting Scheduler
  10. 1272. Remove Interval

C# Technique: Sort with custom comparator: Array.Sort(intervals, (a, b) => a[0].CompareTo(b[0]))

Phase 3: Advanced Patterns (Weeks 21-35)

✅ Pattern 12: Linked List

Goal: Master pointer manipulation

Problems to Master: 12-15 problems

Core Concepts:

  • Dummy node technique
  • Fast-slow pointers
  • Reversal

Problem Set:

  1. 206. Reverse Linked List - Must know
  2. 21. Merge Two Sorted Lists
  3. 141. Linked List Cycle
  4. 142. Linked List Cycle II
  5. 876. Middle of the Linked List
  6. 19. Remove Nth Node From End of List
  7. 2. Add Two Numbers
  8. 92. Reverse Linked List II
  9. 25. Reverse Nodes in k-Group
  10. 234. Palindrome Linked List
  11. 143. Reorder List
  12. 148. Sort List - Merge sort
  13. 146. LRU Cache - Very important

C# Note: Use LinkedListNode<T> or create custom ListNode class

✅ Pattern 13: Tree Traversals (DFS)

Goal: Preorder, Inorder, Postorder

Problems to Master: 15-20 problems

Core Concepts:

  • Recursive vs iterative
  • When to process node (pre/in/post)
  • Divide and conquer

Problem Set (Preorder):

  1. 226. Invert Binary Tree
  2. 100. Same Tree
  3. 572. Subtree of Another Tree
  4. 297. Serialize and Deserialize Binary Tree

Problem Set (Inorder):

  1. 94. Binary Tree Inorder Traversal
  2. 98. Validate Binary Search Tree
  3. 230. Kth Smallest Element in a BST
  4. 173. Binary Search Tree Iterator

Problem Set (Postorder):

  1. 543. Diameter of Binary Tree
  2. 124. Binary Tree Maximum Path Sum
  3. 110. Balanced Binary Tree
  4. 236. Lowest Common Ancestor of a Binary Tree

Problem Set (Divide & Conquer):

  1. 105. Construct Binary Tree from Preorder and Inorder Traversal
  2. 108. Convert Sorted Array to Binary Search Tree
  3. 235. Lowest Common Ancestor of a Binary Search Tree

Master tree recursion - it's everywhere!

✅ Pattern 14: Tree BFS (Level Order)

Goal: Process trees level by level

Problems to Master: 8-10 problems

Core Concepts:

  • Queue-based traversal
  • Track level size
  • Right side view

Problem Set:

  1. 102. Binary Tree Level Order Traversal
  2. 103. Binary Tree Zigzag Level Order Traversal
  3. 199. Binary Tree Right Side View
  4. 104. Maximum Depth of Binary Tree
  5. 662. Maximum Width of Binary Tree
  6. 314. Binary Tree Vertical Order Traversal
  7. 863. All Nodes Distance K in Binary Tree

✅ Pattern 15: Heap / Priority Queue

Goal: Top K, merge K, sliding window median

Problems to Master: 10-12 problems

Core Concepts:

  • Min heap / Max heap
  • Maintain top K elements
  • Two heaps technique

Problem Set:

  1. 215. Kth Largest Element in an Array
  2. 347. Top K Frequent Elements
  3. 973. K Closest Points to Origin
  4. 23. Merge k Sorted Lists
  5. 295. Find Median from Data Stream - Two heaps
  6. 373. Find K Pairs with Smallest Sums
  7. 378. Kth Smallest Element in a Sorted Matrix
  8. 1235. Maximum Profit in Job Scheduling
  9. 1094. Car Pooling
  10. 630. Course Schedule III

C# Data Structure: PriorityQueue<TElement, TPriority> (.NET 6+)

✅ Pattern 16: Recursion & Backtracking

Goal: Generate all possibilities

Problems to Master: 12-15 problems

Core Concepts:

  • Decision tree
  • Choose → Explore → Unchoose
  • Base case

Problem Set (coming from repo - will extract from [J]recursion section)

Focus on: Subsets, Permutations, Combinations, N-Queens, Sudoku Solver

This is the most challenging pattern - take your time!

Phase 4: Expert Level (Weeks 36-52)

✅ Pattern 17: Dynamic Programming

Goal: Optimize recursive solutions

Problems to Master: 20+ problems (this is huge!)

Sub-patterns:

  • 1D DP (Climbing stairs, House Robber)
  • 2D DP (Grid paths, LCS, Edit Distance)
  • Knapsack variants
  • DP on strings

Dedicate 2-3 months to this pattern alone!

✅ Pattern 18: Graph (BFS/DFS)

Goal: Traverse graphs, find paths

Problems to Master: 15+ problems

Core Concepts:

  • Adjacency list representation
  • Visited set
  • Connected components
  • Cycle detection

✅ Pattern 19: Trie

Goal: Prefix-based operations

Problems to Master: 8-10 problems

✅ Pattern 20: Union Find

Goal: Connected components, cycle detection

Problems to Master: 8-10 problems

🔄 Biweekly Revision Schedule

Every 2 weeks, solve:

  • 2 problems from oldest mastered pattern
  • 1 problem from second oldest mastered pattern

Example (Week 10):

  • You've mastered: Array Basics, Two Pointers (Same), Two Pointers (Opposite)
  • This weekend: Solve 2 Array problems + 1 Two Pointer (Same) problem

🎯 Success Metrics

After 1 year:

  • ✅ Mastered 15-18 core patterns
  • ✅ Solved 300-400 problems total
  • ✅ Can identify pattern in 80% of new problems
  • ✅ Confident in Medium problems, can attempt Hard
  • ✅ Ready for any coding interview

💡 Pro Tips

  1. Don't rush - 10 problems per pattern minimum
  2. Understand, don't memorize - Can you explain the approach?
  3. Code in C# without looking - True mastery test
  4. Time yourself - 30 min for Easy, 45 for Medium
  5. Review mistakes - Keep a "mistakes journal"
  6. Teach someone - Best way to solidify learning

🤝 Join Me on This Journey

I haven't started yet, but I will. And when I do, I'll update this post with:

  • My progress updates
  • Problems that really helped me "click"
  • Pitfalls to avoid
  • Time estimates for each pattern

If you're using this plan, drop a comment! Let's learn together.

🙏 Credits

This plan was created with assistance from Claude AI. I provided my constraints (limited time, need for structure, C# preference), and together we crafted something that actually feels doable.

The lesson? Don't be afraid to use AI as your learning companion. It won't solve problems for you, but it can help you create a roadmap that respects your reality.

Tags: #dsa #datastructures #algorithms #leetcode #learning #csharp #career

Bookmark this if you're also planning to start "someday" 📚✨

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