Delete all users with `role: "spam"`, set remaining users `verified` to `true`, then return distinct roles.

Problem Statement

<p>Delete all <code>users</code> with <code>role: "spam"</code>, set remaining <code>users</code> <code>verified</code> to <code>true</code>, then return distinct roles.</p>

Examples

Explanation: The target document is modified according to the update operators and the updated document is returned.

Complexity

Time Complexity: -

Space Complexity: -

Hints

💡 Hint 1: Use db.<collection>.find(<filter>) to query the documents in the collection. 💡 Hint 2: Pass an empty object {} to retrieve all documents, or specify key-value pairs for exact matching. 💡 Hint 3: Chain .toArray() to resolve the MongoDB cursor into a JavaScript array: return db.<collection>.find(...).toArray();

Editorial & Approach

Problem Overview & Intuition

To solve "Data Cleanup: Remove + Update + Report", we query the MongoDB document store. The goal is to delete all users with `role: "spam"`, set remaining users `verified` to `true`, then return distinct roles. Using a targeted find query, the database engine filters and structures the BSON documents efficiently.

Step-by-Step Approach

Identify Target Collection: Access the collection through the db instance.
Construct Query / Pipeline: Build the query filter with appropriate comparison operators.
Resolve Cursor: Invoke .toArray() to transform the query cursor into the required array of documents.

Optimal Implementation (MongoDB)

function solve(db) {
  db.users.deleteMany({ role: "spam" });
  db.users.updateMany({}, { $set: { verified: true } });
  return db.users.distinct("role");
}

Complexity Analysis

Time Complexity O(N) collection scan (O(log N) if index is present on filtered fields).

Space Complexity O(K) where K is the number of returned documents in memory.

Key Considerations & Edge Cases

Empty Collections: If no documents match, the query cleanly returns an empty array [].
Missing / NULL Fields: Missing fields in documents are handled safely without throwing runtime exceptions.
Type Coercion: BSON types (ObjectId, Numbers, Strings) are compared strictly according to MongoDB specifications.

Data Cleanup: Remove + Update + Report

Hard

Delete all users with role: "spam", set remaining users verified to true, then return distinct roles.

Example Scenarios

1Example 1

Input:

users collection

_id	name	role	verified
1	Alice	admin	false
2	Spammer1	spam	false
3	Bob	user	false
4	Spammer2	spam	false
5	Charlie	user	false

Output:

result
admin
user

Explanation:

The target document is modified according to the update operators and the updated document is returned.

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Query Results (JSON)

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