DSA Mastery Notes (Free Resources + 14 Patterns)

DSA Mastery Notes

(Free Resources + 14 Patterns)

Best Free Resources to Learn DSA

1. YouTube Channels

• Striver (takeUforward) → Complete DSA + Placement Series
  🔗 https://www.youtube.com/c/takeUforward

• Love Babbar → DSA in Hindi (450 DSA Sheet)
  🔗 https://www.youtube.com/c/LoveBabbar

• Kunal Kushwaha → Beginner to Advanced DSA + Open Source
  🔗 https://www.youtube.com/c/KunalKushwaha

• CodeWithHarry → DSA + Java + Python
  🔗 https://www.youtube.com/c/CodeWithHarry

2. Free Platforms for Practice

• LeetCode (Free Tier) → https://leetcode.com
• GeeksForGeeks (Free Articles + Practice) → https://www.geeksforgeeks.org
• CodeStudio (Coding Ninjas) → https://www.codingninjas.com/codestudio
• InterviewBit → https://www.interviewbit.com
• HackerRank → https://www.hackerrank.com/domains/tutorials/10-days-of-javascript

3. Free DSA Roadmaps

• Striver’s SDE Sheet
  🔗 https://takeuforward.org/interviews/strivers-sde-sheet-top-coding-interview-problems/

• Love Babbar 450 Sheet
  🔗 https://450dsa.com/

• Neetcode.io (Pattern-based DSA)
  🔗 https://neetcode.io/roadmap

14 Core DSA Patterns to Master

Placement-Oriented

Learning DSA by patterns helps you quickly recognize question types and apply the right approach during interviews.

1. Sliding Window
   Used for subarrays/substrings — max sum subarray, longest substring without repeating characters.

2. Two Pointers
   Used for sorted arrays or linked lists — pair sum, remove duplicates.

3. Fast & Slow Pointers
   Detect cycles, find middle of a linked list.

4. Merge Intervals
   For overlapping ranges — meeting rooms, merging intervals.

5. Cyclic Sort
   Finding missing/duplicate numbers in known ranges.

6. In-place Reversal of Linked List
   Reverse a linked list or sublist without extra space.

7. Tree BFS / DFS
   Level order, path sum, lowest common ancestor, etc.

8. Graph BFS / DFS
   Grids, connected components, shortest path (unweighted).

9. Topological Sort
   Task ordering in DAGs — course scheduling, dependencies.

10. Binary Search
    Searching, boundaries, peaks, rotations, monotonic functions.

11. Backtracking
    Combinations, permutations, subsets — N-Queens, Sudoku.

12. Dynamic Programming (DP)
    Optimization problems — knapsack, LIS, coin change.

13. Greedy Algorithms
    Optimal local choices — activity selection, Huffman coding.

14. Heap / Priority Queue
    Kth largest/smallest, top K elements, merge sorted arrays.

Recommended Learning Order

• Arrays & Strings
  (Sliding Window, Two Pointers)
• Linked Lists
  (Reversal, Fast/Slow Pointers)
• Stacks & Queues
  (Next Greater Element, Balanced Parentheses)
• Trees & Graphs
  (DFS, BFS, Topological Sort)
• Binary Search + Recursion
• Backtracking
• Dynamic Programming
• Heaps & HashMaps
• Greedy Algorithms

Placement Tip

“DSA isn’t about memorizing questions — it’s about recognizing patterns.”

• ✅ Focus on 1–2 patterns per week
• ✅ Practice 3–5 questions per pattern
• ✅ Revisit mistakes regularly