Write a function `flattenObject(obj)` that flattens a nested object using dot notation for keys.

Problem Statement

<p>Write a function <code>flattenObject(obj)</code> that flattens a nested object using dot notation for keys.</p>

Examples

Input: obj = { a: { b: { c: 1 } }, d: 2 }

Output: { "a.b.c": 1, d: 2 }

Explanation: Nested hierarchy converted to dot notation keys.

Complexity

Time Complexity: O(N)

Space Complexity: O(1)

Hints

💡 Hint 1: Use recursion to traverse nested objects. 💡 Hint 2: Concatenate parent key and child key with a dot. 💡 Hint 3: If a value is an object (not null, not array), recurse. Otherwise assign to the flattened key.

Editorial & Approach

Problem Overview & Intuition

To solve Flatten Object, we consider the execution characteristics of JavaScript engines. Write a function `flattenObject(obj)` that flattens a nested object using dot notation for keys. By utilizing idiomatic language constructs and clean algorithmic principles, we can accomplish this with optimal time and memory usage.

Step-by-Step Approach

Understand Problem Contract: Identify input arguments, return type expectations, and edge cases (empty inputs, nullish values).
Choose Core Mechanism: Use modern JavaScript patterns (use recursion to traverse nested objects).
Implement Logic: Handle state and transformations efficiently (concatenate parent key and child key with a dot).
Return Result: Ensure proper return format and preserve caller context if applicable.

Optimal Implementation (JavaScript)

function flattenObject(obj, prefix = "", result = {}) {
  for (const key of Object.keys(obj)) {
    const newKey = prefix ? `${prefix}.${key}` : key;
    if (typeof obj[key] === "object" && obj[key] !== null && !Array.isArray(obj[key])) {
      flattenObject(obj[key], newKey, result);
    } else {
      result[newKey] = obj[key];
    }
  }
  return result;
}

Complexity Analysis

Time Complexity O(N) linear scan over input

Space Complexity O(1) constant auxiliary space (or O(N) output)

Edge Cases & Corner Traps Handled

Empty or boundary inputs (empty arrays, strings, zero length).
Type checks and unexpected values (e.g. null, undefined, negative numbers).
Closure preservation and memory isolation between separate invocations.

Flatten Object

Medium

Write a function flattenObject(obj) that flattens a nested object using dot notation for keys.

Example Scenarios

1Example 1

Input: obj = { a: { b: { c: 1 } }, d: 2 }

Output: { "a.b.c": 1, d: 2 }

Explanation:

Nested hierarchy converted to dot notation keys.

Editor

Loading Editor...

Evaluate code

Output:Click "Run" above to execute and verify your code here.

{"a":1,"b.c":2,"b.d.e":3,"f":4}