DSA Basics

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TOPIC NAME: Basics

1. ABOUT THE TOPIC

• DSA basics are the mental tools you use before picking any advanced data structure or algorithm.
• This topic matters because interviews usually test your thinking process, complexity awareness, and ability to choose the right approach before code.
• In interviews, basics show up when you explain brute force, optimize a solution, discuss constraints, and handle corner cases.

2. KEY CONCEPTS

• Time Complexity: Measures how runtime grows with input size, usually written with Big O.
• Space Complexity: Tracks extra memory used by the algorithm, not just the input itself.
• Input Constraints: Help decide whether brute force, sorting, hashing, recursion, or DP is even feasible.
• Dry Run: A manual simulation that helps catch logic bugs and edge cases early.
• Brute Force to Optimal: The standard interview flow is to first state the simple solution, then improve it.

3. COMMON PATTERNS

• Brute Force Baseline: Start with the simplest correct idea to establish correctness.
• Hashing: Use maps or sets when you need fast lookup or frequency counting.
• Sorting First: Sort when order helps reduce comparisons or enables greedy and two-pointer logic.
• Precomputation: Prefix arrays, frequency tables, or memo tables help avoid repeated work.

4. COMPLEXITY GUIDE

• O(1), O(log n), O(n), and O(n log n) are usually safe for large interview constraints.
• O(n^2) may work for small n, but you should always compare against the constraint before finalizing.
• Prefer in-place solutions when possible, but do not sacrifice clarity or correctness unnecessarily.
• When using recursion, include call-stack space in your analysis.

5. QUESTIONS (WITH LINKS)

EASY:

• Palindrome Number
  Link: https://leetcode.com/problems/palindrome-number/

• Reverse Integer
  Link: https://leetcode.com/problems/reverse-integer/

• Fizz Buzz
  Link: https://leetcode.com/problems/fizz-buzz/

MEDIUM:

• Evaluate Reverse Polish Notation
  Link: https://leetcode.com/problems/evaluate-reverse-polish-notation/

• Compare Version Numbers
  Link: https://leetcode.com/problems/compare-version-numbers/

HARD:

• Basic Calculator
  Link: https://leetcode.com/problems/basic-calculator/

6. INTERVIEW TIPS

• Do not jump into code before checking constraints and examples.
• Always say the brute force idea first, then explain why it is slow.
• Use small dry runs to verify indexing, overflow risk, and empty input behavior.
• Mention tradeoffs clearly when you choose readability over strict in-place optimization.

7. PRACTICE STRATEGY

• Start with complexity analysis and dry-run based problems.
• Solve a few simple implementation tasks to improve coding speed.
• Then revisit solved problems and practice explaining brute force, better, and optimal versions aloud.

8. BLOG SEO META

• Title: DSA Basics for Interviews | Complexity, Problem Solving, and Core Patterns
• Description: Learn the DSA basics every beginner needs: time complexity, space complexity, brute force thinking, dry runs, and interview-friendly problem solving.
• Keywords: DSA basics, Big O notation, coding interview basics, Striver A2Z basics, problem solving patterns