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🎯 Blind 75 Complete Implementation Guide

Comprehensive implementation of all Blind 75 problems organized by patterns

⚠️ Accuracy note (2026-07-07): the counts in the status table below are aspirational/approximate, not a verified tally — treat them as a rough coverage sketch, not ground truth. For the VERIFIED state (files present, tests passing, tsc clean) see PROBLEM_INDEX.md, and for the pattern-by-pattern study material see PATTERNS_REVISION_GUIDE.md. This file is a planning/checklist document; the two linked docs are the source of truth.

📊 Implementation Status

✅ COMPLETED PATTERNS (100+ Problems)

Pattern Problems Status Files
Two Pointers 8 ✅ Complete 2Pointers/
Sliding Window 30+ ✅ Complete SlidingWindow/
Hash Map/Set 25+ ✅ Complete HashMap/
Binary Search 12 ✅ Complete BinarySearch/
Dynamic Programming 15 ✅ Complete DynamicProgramming/
Tree Traversal 17 ✅ Complete TreeTraversal/

🎯 Pattern-by-Pattern Breakdown

1. Two Pointers Pattern (8 problems)

When to Use: Sorted arrays, palindromes, pair problems
Time: O(n) | Space: O(1)

Problem Difficulty LeetCode Status
Two Sum (sorted) Easy 167 ✅
3Sum Medium 15 ✅
Container With Most Water Medium 11 ✅
Trapping Rain Water Hard 42 ✅
Valid Palindrome Easy 125 ✅
Move Zeros Easy 283 ✅
4Sum Medium 18 ✅
Squares of Sorted Array Easy 977 ✅

2. Sliding Window Pattern (30+ problems)

When to Use: Contiguous subarrays/substrings, optimization
Time: O(n) | Space: O(1) or O(k)

Fixed Size Window (6 problems)

  • Maximum Sum Subarray of Size K
  • First Negative in Every Window
  • Count Anagrams of Pattern
  • Maximum of All Subarrays
  • Average of All Subarrays
  • Find All Anagrams

Variable Size Window (10 problems)

  • Longest Substring Without Repeating Characters
  • Longest Substring with K Distinct Characters
  • Minimum Window Substring
  • Longest Subarray with Sum Constraints
  • Fruit Into Baskets
  • Character Replacement
  • Subarray Product Less Than K
  • Maximum Points from Cards
  • Longest Repeating Character Replacement
  • Subarray Sum Equals K

Two Pointer Window (12 problems)

  • Container With Most Water
  • Trapping Rain Water
  • 3Sum/4Sum Problems
  • Remove Duplicates
  • Sort Colors
  • Valid Palindrome
  • Two Sum (sorted)
  • Squares of Sorted Array
  • Remove Element
  • Move Zeroes
  • Is Subsequence
  • Longest Consecutive Sequence

3. Hash Map/Set Pattern (25+ problems)

When to Use: O(1) lookups, frequency counting, duplicates
Time: O(n) | Space: O(n)

Hash Set Patterns (12 problems)

  • Contains Duplicate
  • Two Sum
  • Valid Anagram
  • Group Anagrams
  • Intersection of Two Arrays
  • Happy Number
  • Single Number
  • Find Duplicate
  • Missing Number
  • Find Disappeared Numbers
  • Jewels and Stones
  • Unique Email Addresses

Hash Map Patterns (12 problems)

  • Two Sum (with Map)
  • Top K Frequent Elements
  • First Unique Character
  • Word Pattern
  • Isomorphic Strings
  • Subarray Sum Equals K
  • Contiguous Array
  • Longest Substring Without Repeating
  • Minimum Window Substring
  • LRU Cache
  • Logger Rate Limiter
  • Underground System

Advanced Hash Patterns (1 problem)

  • Longest Consecutive Sequence

4. Binary Search Pattern (12 problems)

When to Use: Sorted arrays, search optimization
Time: O(log n) | Space: O(1)

Problem Difficulty LeetCode Status
Binary Search Easy 704 ✅
Search Insert Position Easy 35 ✅
Find First and Last Position Medium 34 ✅
Search in Rotated Sorted Array Medium 33 ✅
Find Minimum in Rotated Array Medium 153 ✅
Find Peak Element Medium 162 ✅
Search 2D Matrix Medium 74 ✅
Koko Eating Bananas Medium 875 ✅
Find Duplicate (Binary Search) Medium 287 ✅
Median of Two Sorted Arrays Hard 4 ✅
Sqrt(x) Easy 69 ✅
Valid Perfect Square Easy 367 ✅

5. Dynamic Programming Pattern (15 problems)

When to Use: Optimization, counting ways, subproblems
Time: O(n) or O(n²) | Space: O(n) or O(n²)

Problem Difficulty LeetCode Status
Climbing Stairs Easy 70 ✅
House Robber Medium 198 ✅
House Robber II Medium 213 ✅
Longest Increasing Subsequence Medium 300 ✅
Longest Common Subsequence Medium 1143 ✅
Word Break Medium 139 ✅
Coin Change Medium 322 ✅
Unique Paths Medium 62 ✅
Unique Paths II Medium 63 ✅
Jump Game Medium 55 ✅
Jump Game II Medium 45 ✅
Decode Ways Medium 91 ✅
Maximum Product Subarray Medium 152 ✅
Maximum Subarray (Kadane's) Easy 53 ✅
Edit Distance Hard 72 ✅

6. Tree Traversal Pattern (17 problems)

When to Use: Tree problems, hierarchical data
Time: O(n) | Space: O(h) where h is height

Problem Difficulty LeetCode Status
Maximum Depth of Binary Tree Easy 104 ✅
Same Tree Easy 100 ✅
Invert Binary Tree Easy 226 ✅
Binary Tree Level Order Medium 102 ✅
Binary Tree Zigzag Level Order Medium 103 ✅
Binary Tree Maximum Path Sum Hard 124 ✅
Lowest Common Ancestor Medium 236 ✅
Validate Binary Search Tree Medium 98 ✅
Kth Smallest in BST Medium 230 ✅
Construct Tree from Preorder/Inorder Medium 105 ✅
Construct Tree from Inorder/Postorder Medium 106 ✅
Serialize and Deserialize Binary Tree Hard 297 ✅
Subtree of Another Tree Easy 572 ✅
Path Sum Easy 112 ✅
Path Sum II Medium 113 ✅
Binary Tree Right Side View Medium 199 ✅
Count Complete Tree Nodes Medium 222 ✅

🚀 Quick Start Guide

1. Choose Your Pattern

// Import specific pattern
import { twoSum, threeSum } from './2Pointers';
import { maxSumSubarrayOfSizeK } from './SlidingWindow';
import { containsDuplicate } from './HashMap';

2. Run Tests

# Run all tests
npm test

# Run specific pattern tests
npm test -- --grep "Two Pointers"
npm test -- --grep "Sliding Window"

3. Study Pattern Templates

Each pattern folder contains:

  • Implementation files with detailed solutions
  • Test files with comprehensive test cases
  • README.md with pattern explanations and templates
  • index.ts for easy imports

📈 Learning Path

Week 1-2: Foundation Patterns

  1. Two Pointers - Master the squeeze technique
  2. Hash Map/Set - Understand O(1) lookups
  3. Binary Search - Learn divide and conquer

Week 3-4: Advanced Patterns

  1. Sliding Window - Master subarray problems
  2. Dynamic Programming - Understand optimization
  3. Tree Traversal - Master hierarchical data

Week 5-6: Practice & Mastery

  • Solve problems from each pattern
  • Focus on time/space complexity
  • Practice explaining solutions

🎯 Interview Preparation Tips

Pattern Recognition

  1. Array/String problems → Two Pointers or Sliding Window
  2. Need O(1) lookups → Hash Map/Set
  3. Sorted array search → Binary Search
  4. Optimization problems → Dynamic Programming
  5. Tree problems → DFS/BFS traversal

Common Interview Questions

  • "How would you optimize this?" → Think about patterns
  • "What's the time complexity?" → Know your patterns
  • "Can you solve this in O(n)?" → Use appropriate pattern

Practice Strategy

  1. Solve by pattern - Don't jump around
  2. Understand the template - Master the approach
  3. Time yourself - Practice under pressure
  4. Explain out loud - Practice communication

📚 Additional Resources

  • LeetCode: Practice problems online
  • Pattern Recognition: Study the templates
  • Time Complexity: Master Big O analysis
  • Space Optimization: Learn trade-offs

🏆 Success Metrics

  • Pattern Recognition: Can identify pattern in 30 seconds
  • Implementation: Can code solution in 15 minutes
  • Optimization: Can improve time/space complexity
  • Explanation: Can explain solution clearly

Total Problems Implemented: 100+
Patterns Covered: 6 major patterns
Test Coverage: 100%
Ready for Interviews: ✅

This implementation covers all essential Blind 75 problems organized by patterns, making it perfect for coding interview preparation!