Day6.md

📅 Day 6 – Reflection

🔥 Theme: Relentless Consistency – One Day Stronger!

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✅ Task 1: DSA – Longest Substring Without Repeating Characters

Problem:
→ LeetCode: Longest Substring Without Repeating Characters

What I did:
✔ Solved using Boolean array (26-length) → faced IndexOutOfBounds
✔ Refactored with HashSet (Sliding Window) → ✅ Accepted
✔ Learned two variations of solving:
  - Array-based
  - HashSet-based (cleaner, scalable)

What I learned:

• Sliding Window
• Common trap with character arrays
• Importance of correct array size (ASCII → use 128)
• Clean code using HashSet

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✅ Task 2: Core CS – DBMS Transactions & ACID

Topics Studied:

• ACID properties: Atomicity, Consistency, Isolation, Durability
• Transaction states: Active, Partially Committed, Failed, Aborted, Committed, Terminated
• Basic intro to concurrency control problems

Reflection:
✔ Concepts were a bit abstract, but got the gist
✔ Atomicity & Durability made good sense
✔ Realized why transactions are the backbone of reliable systems

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✅ Task 3: Python – Data Modeling (Superstore ETL)

What I did:

• Used Superstore dataset again
• Performed grouping & aggregation:
  • Total Sales and Profit
  • Number of unique Orders per Customer
  • Sort values based on Total Profit in Descending order
• Exported clean CSVs (✔ customer_profitability.csv)

Reflection:
✔ Reinforced real-world ETL + aggregation flow
✔ Confidence building with pandas pipelines

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✅ Task 4: SQL – Mini Data Mart Queries

Completed:

1. ✅ Most popular product by number of orders
2. ✅ Revenue by region
3. ✅ Average order size by customer

Reflection:
✔ Learned how to use JOIN, GROUP BY, COUNT, and subqueries for real business questions
✔ Practiced using realistic INSERTs and data design
✔ Strengthened skill in translating questions into SQL

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Summary

✅ DSA: Sliding Window + HashSet Problem
✅ DBMS: ACID properties, Transaction states, Concurrency Control problems
✅ Python: Data modeling
✅ SQL: Joins and Aggregation