Скачать или смотреть Hashing & HashMap MASTERCLASS - Solve 25+ Coding Interview Problems | Pattern-Based Approach

Hashing is arguably the MOST IMPORTANT technique in coding interviews. It turns O(n²) solutions into O(n) and solves problems that seem impossible otherwise. In this ultimate tutorial, we'll solve 25+ diverse problems using HashMaps, HashSets, and frequency counting—grouped by pattern so you build intuition, not just memorize solutions.

📚 Comprehensive Problem List (with Timestamps):

Module 1: The Foundation - Classic HashMap Problems
00:00 - Introduction: Why Hashing is a Superpower
02:30 - 1. Two Sum (The Granddaddy of all HashMap problems)
05:45 - 2. Find the Difference (Frequency counting basics)
08:20 - 3. Check if N and its Double exist (Two approaches)
11:15 - 4. How many Numbers are Smaller than current number (Optimization trick)

Module 2: Prefix Sum & Subarray Problems (Game-Changer!)
14:30 - 5. Subarray with 0 sum (The "prefix sum in hashset" pattern)
18:45 - 6. Subarray Sum Equals K (Critical! Frequency map of prefix sums)
23:30 - 7. Largest Continuous Sequence Zero Sum (Storing indices)
27:15 - 8. Minimum Size Subarray Sum (Sliding window + prefix sum optimization)

Module 3: String Manipulation & Frequency Analysis
30:40 - 9. Find the Difference (Char frequency deep dive)
33:20 - 10. Maximum Number of Balloons (Word composition pattern)
36:10 - 11. Anagrams (Multiple approaches compared)
40:25 - 12. Decode the Message (Character mapping with HashMaps)
43:50 - 13. Palindrome Pairs (Advanced string hashing)

Module 4: Matrix & Grid Problems
47:30 - 14. Valid Sudoku (Efficient validation with HashSets)
51:20 - 15. Set Matrix Zeros (Space-optimized using hashing)
55:10 - 16. Grid Illumination (LeetCode hard - diagonal tracking trick)
1:00:30 - 17. Find rectangle with corners as 1 (Smart pair caching)

Module 5: Advanced Patterns & Combinatorial Problems
1:04:45 - 18. Fair Candy Swap (Mathematical insight + HashSet)
1:08:20 - 19. Find Pairs In Array Whose Sums Already Exist (Multiple sums caching)
1:12:10 - 20. Longest Consecutive Sequence (The O(n) boundary trick)
1:16:35 - 21. Equal (HackerRank problem - frequency transformation)
1:20:50 - 22. Window String (Minimum window substring pattern)
1:25:30 - 23. Longest Substring Without Repeat (Sliding window + HashMap)

Module 6: Geometric & Mathematical Hashing
1:29:15 - 24. Points on same line (Slope hashing - handle precision!)
1:34:40 - 25. Count Right Triangles (Coordinate frequency approach)
1:38:10 - 26. Diffk II (Pair difference problem)

Module 7: System Design & Randomized Hashing
1:41:25 - 27. Random Pick with Blacklist (Clever remapping technique)
1:45:00 - 28. Sum of Unique Elements (Simple but important pattern)

Module 8: Putting It All Together
1:47:30 - 29. Hashing Quiz - Test your pattern recognition!
1:51:45 - 30. HackerRank Test Walkthrough - Full problem-solving session
1:56:20 - Cheat Sheet & Final Thoughts

🎯 7 Hashing Patterns You'll Master:
1️⃣ Frequency Counting (Arrays, Strings)
2️⃣ Prefix Sum + HashMap (Subarray sums problems)
3️⃣ Two-Pass Hashing (Preprocessing for O(1) lookups)
4️⃣ Sliding Window + HashMap (Substring problems)
5️⃣ Coordinate/Geometric Hashing (Slopes, pairs, triangles)
6️⃣ Character/Word Mapping (Anagrams, substitutions)
7️⃣ Mathematical Relation Hashing (Equations, differences)

👨💻 Perfect For:

Developers preparing for Google, Meta, Amazon interviews

Competitive programmers optimizing for time complexity

Computer science students learning data structures

Anyone who wants to think more efficiently about problem-solving

💡 Key Takeaways:

When to use HashMap vs HashSet vs frequency array

How to handle collision scenarios in geometric problems

Space-time tradeoffs in different hashing approaches

Real interview patterns and how to recognize them instantly

💻 Languages Used:
Solutions explained conceptually with implementations in Python (dictionaries) and Java (HashMaps). The patterns apply to any language!

🚀 Engage With The Community:

COMMENT below: Which hashing pattern was most surprising to you?

LIKE if you found the "Prefix Sum + HashMap" pattern revolutionary!

Tags :
#Hashing #HashMap #CodingInterview #DataStructures #LeetCode #Python #Java #Algorithm #Programming #FAANG #HashSet #FrequencyCount #SubarraySum #TwoSum #TechInterview #ProblemSolving #SoftwareEngineer #ComputerScience #HackerRank #codinginterview