Count Character/Element Frequency

📌 Definition:

📖 Detailed Explanation:

Iterate once, incrementing a counter per item using reduce or a for-of loop. Use a Map when keys may collide with object prototype names, otherwise a plain object is fine.

💻 Solutions:

• JavaScript

function frequency(items) {
  return [...items].reduce((acc, x) => {
    acc[x] = (acc[x] || 0) + 1;
    return acc;
  }, {});
}

🔑 Key Points:

• (acc[x] || 0) + 1 initializes and increments in one step
• O(n) single pass
• Use a Map to avoid prototype-key collisions (e.g. 'constructor')
• [...items] works for strings and arrays

🌍 Real-World Example: