🧠 40-Day Algorithm & LeetCode Learning Review

🗓️ Overview

You've just completed 40 days of algorithm mastery, ranging from beginner to advanced LeetCode problems — from arrays, strings, two pointers, and sliding windows to binary search, recursion, dynamic programming (DP), and more!

🧱 Foundation Topics (Days 1–10)

• Big-O Notation: Analyzed time and space complexity.
• Arrays & Strings: Hands-on with iteration, index access, and reverse operations.
• Two Pointers: Efficient techniques for problems like sorted arrays, palindromes.
• Sliding Window: For subarrays and strings (max sum, longest unique substring).

✅ Skills Gained:

• Optimizing loops
• Avoiding brute-force
• Early pattern recognition

🔁 Recursion to Binary Search (Days 11–20)

• Recursion: Base cases and call stacks visualized.
• Binary Search: Classical, rotated arrays, and search boundaries.
• Prefix Sums & 2D Grids: Fast sum range queries and matrix manipulations.

✅ Skills Gained:

• Recursion tracing
• Optimizing with pre-processing
• Matrix intuition

🔄 Intermediate Patterns (Days 21–30)

• Backtracking: Permutations, combinations, subset generation.
• Dynamic Programming (Easy–Medium):
  • Fibonacci (top-down & bottom-up)
  • House Robber
  • Climbing Stairs variations
• Greedy Thinking: Making the locally optimal choice (Jump Game).

✅ Skills Gained:

• State storage with DP arrays
• Recursive thinking to iterative translation
• Pattern generalization

🧠 Advanced Patterns & DP (Days 31–40)

• Partitioning & State Transitions: Decode Ways, Coin Change, Longest Palindromic Substring.
• Interval DP: Matrix Chain Multiplication, Burst Balloons
• Knapsack Variation: 0/1 and Unbounded Knapsack

✅ Skills Gained:

• Breaking down overlapping subproblems
• Thinking in ranges and partitions
• Space optimization techniques

📘 Key Learning Patterns

• DP Formulas: dp[i], dp[i][j], and transitions
• Memoization vs Tabulation
• Two Pointer Sliding Strategy
• Binary Search on Answer
• Backtracking Trees

🔍 Tips Going Forward

1. Review your weak spots with a second round.
2. Start daily LeetCode practice: mix difficulty levels.
3. Build a digital note/bookmark of patterns.
4. Begin mock interviews and timed contests.

🧪 Self-Test Challenge

Try solving one problem from each of these categories:

• Sliding Window
• Binary Search (Rotated Array)
• Backtracking (Subsets)
• DP (Knapsack or Palindromes)
• Interval DP (Burst Balloons)

🔮 Up Next

▶️ Day 41: Bit Manipulation — Single Number Problems

You're leveling up — and now it’s time to explore the magic of bits 🧮!