Flatten and Unflatten a Nested Object (dot notation & arrays)

Question

Accepted Answer

**Approach:** DFS to flatten, building `prefix.key`; for unflatten, split by `.` and build nested structure, detecting numeric keys for arrays.

```javascript
function flattenObject(obj, prefix = '', res = {}) {
  for (const [k, v] of Object.entries(obj)) {
    const key = prefix ? `${prefix}.${k}` : k;
    if (v !== null && typeof v === 'object' && !Array.isArray(v) && !(v instanceof Date)) {
      flattenObject(v, key, res);
    } else if (Array.isArray(v)) {
      v.forEach((item, i) => {
        const ak = `${key}.${i}`;
        if (item !== null && typeof item === 'object') flattenObject({ [i]: item }, key, res);
        else res[ak] = item;
      });
      if (v.length === 0) res[key] = [];
    } else res[key] = v;
  }
  return res;
}
function unflattenObject(flat) {
  const res = {};
  for (const [path, val] of Object.entries(flat)) {
    const keys = path.split('.');
    let cur = res;
    for (let i = 0; i < keys.length; i++) {
      const k = keys[i]; const isLast = i === key

Flatten and Unflatten a Nested Object (dot notation & arrays)

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Understand the problem

Attempt it yourself

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Join the discussion

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KEEP THESTREAK ALIVE.

KEEP THE
STREAK ALIVE.