Find all movies with a `genre` of either `"Action"` or `"Sci-Fi"`.

Problem Statement

<p>Find all <code>movies</code> with a <code>genre</code> of either <code>"Action"</code> or <code>"Sci-Fi"</code>.</p>

Examples

Explanation: Documents containing the matching array elements are selected from the collection.

Complexity

Time Complexity: -

Space Complexity: -

Hints

💡 Hint 1: Filter documents where a field matches any value in a list using the $in or $nin operator. 💡 Hint 2: Pass the query object to db.<collection>.find({ field: { $in: [val1, val2, ...] } }). 💡 Hint 3: Call .toArray() on the returned cursor so the function returns the array of matching documents.

Editorial & Approach

Problem Overview & Intuition

To solve "In Array ($in)", we query the MongoDB document store. The goal is to find all movies with a `genre` of either `"action"` or `"sci-fi"`. 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) {
  return db.movies.find({ genre: { $in: ["Action", "Sci-Fi"] } }).toArray();
}

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.

In Array ($in)

Easy

Find all movies with a genre of either "Action" or "Sci-Fi".

Example Scenarios

1Example 1

Input:

movies collection

_id	title	genre
1	Inception	Sci-Fi
2	Titanic	Drama
3	Mad Max	Action
4	Interstellar	Sci-Fi

Output:

_id	title	genre
1	Inception	Sci-Fi
3	Mad Max	Action
4	Interstellar	Sci-Fi

Explanation:

Documents containing the matching array elements are selected from the collection.

MongoDB Editor

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Query Results (JSON)

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