Delete all inactive users (`active: false`) from `users`, then count how many active users remain.

Problem Statement

<p>Delete all inactive <code>users</code> (<code>active: false</code>) from <code>users</code>, then count how many active <code>users</code> remain.</p>

Examples

Input: users collection: +-----+---------+--------+ | _id | name | active | +-----+---------+--------+ | 1 | Alice | true | | 2 | Bob | false | | 3 | Charlie | true | | 4 | Dana | false | | 5 | Eve | true | +-----+---------+--------+

Output: +-------+ | count | +-------+ | 3 | +-------+

Explanation: The query calculates the total count of documents that satisfy the given filter criteria.

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 "Delete Then Count", we query the MongoDB document store. The goal is to delete all inactive users (`active: false`) from `users`, then count how many active users remain. 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({ active: false });
  return db.users.countDocuments({});
}

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.

Delete Then Count

Medium

Delete all inactive users (active: false) from users, then count how many active users remain.

Example Scenarios

1Example 1

Input:

users collection

_id	name	active
1	Alice	true
2	Bob	false
3	Charlie	true
4	Dana	false
5	Eve	true

Output:

count
3

Explanation:

The query calculates the total count of documents that satisfy the given filter criteria.

MongoDB Editor

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Query Results (JSON)

Run your MongoDB code to see results here.