Overview
This lecture discusses the role of LeetCode problems in programming interviews, strategies for effective practice, and step-by-step solutions to common algorithm challenges like Two Sum, Contains Duplicate, and Valid Anagram.
Introduction to LeetCode & Mindset
- LeetCode is a popular platform for practicing coding interview problems.
- Many perceive LeetCode negatively, but it trains problem-solving and decomposition, not just memorization.
- Treat LeetCode as brain training, similar to puzzles like Sudoku.
- Focus on understanding problem types and building intuition over time.
- Follow a structured roadmap (e.g., arrays then hashing) to avoid overwhelm.
Approaching LeetCode Problems
- Don’t randomly jump between problems; progress through related topics.
- Use resources like NeetCode.io for organized learning paths.
- Practice by solving a problem, then attempt similar variants to reinforce learning.
Example: Two Sum Problem
- Problem: Given an array of numbers and a target, return indices of two numbers that add up to the target.
- Brute-force solution: Use two loops to check all pairs; time complexity is O(n^2).
- Optimized solution: Use a map to store numbers and their indices; for each number, check if the difference (target - number) exists in the map; this reduces time complexity to O(n).
Example: Contains Duplicate
- Problem: Check if an array contains any duplicates.
- Brute-force solution: Use two loops to compare all elements.
- Optimized solution: Use a set to track unique values; if a duplicate appears, return true immediately; otherwise, return false after iterating.
Example: Valid Anagram
- Problem: Determine if two strings are anagrams (can be rearranged to match each other).
- First, check if the strings are the same length; if not, return false.
- Solution 1: Use a map to count character occurrences, decrementing as you traverse the second string; if all counts return to zero, it's an anagram.
- Solution 2: Sort both strings and compare; if equal, they are anagrams.
Key Terms & Definitions
- LeetCode — an online platform for coding interview practice.
- Brute-force — straightforward but inefficient method (checks all possibilities).
- Time Complexity — measure of algorithm efficiency, commonly O(n), O(n^2), etc.
- Hash Map / Map — a data structure that stores key-value pairs for quick lookup.
- Set — a data structure that stores unique values.
- Anagram — a word formed by rearranging the letters of another.
Action Items / Next Steps
- Start LeetCode practice with structured topics (arrays, hashing).
- Try solving Two Sum, Contains Duplicate, and Valid Anagram with both brute-force and optimized methods.
- Review solutions and compare with other users’ approaches after solving.
- Use additional resources like NeetCode.io for learning paths.
- Optional: Explore Brilliant.org for hands-on problem-solving practice.