Arrays, Stacks & Hash Maps

What You'll Cover Today

Day 1 of Data Structures & Algorithms focuses on arrays, stacks & hash maps. Big O notation, arrays, stacks, queues, hash maps with code. This lesson gives you the conceptual foundation and a hands-on exercise so you leave with real working knowledge, not just theory.

Big O

Understanding big o is foundational for everything in this course. The core idea is straightforward once you see it in practice: most complexity comes from edge cases, not the happy path. Start by getting the basic case working, then handle edge cases one at a time.

// Arrays, Stacks & Hash Maps — working example
// Replace these values with your actual data

const example = {
  topic: 'Big O',
  day: 1,
  course: 'Data Structures & Algorithms'
};

// This is where your implementation goes
function implement(config) {
  // 1. Validate inputs
  if (!config.topic) throw new Error('Topic required');
  
  // 2. Core logic
  const result = process(config);
  
  // 3. Return structured output
  return result;
}

console.log('Ready to implement Big O');

hash map

Once you have the basics, hash map becomes the practical application. The pattern you'll use most often is: configure once, reuse everywhere. Avoid copy-pasting implementation details — abstract the repetitive parts into functions or classes.

Common Mistakes on Day 1

• Skipping error handling — every real-world implementation needs error handling. Add it from the start, not as an afterthought.
• Hard-coding configuration — use environment variables for anything that differs between development and production.
• Not reading error messages — error messages in Data are usually precise. Read them carefully before searching Stack Overflow.
• Over-abstracting too early — make it work first, then refactor. Premature abstraction is the enemy of progress.