Find all temperatures between `20` (inclusive) and `30` (exclusive) from the `readings` collection.

Problem Statement

<p>Find all temperatures between <code>20</code> (inclusive) and <code>30</code> (exclusive) from the <code>readings</code> collection.</p>

Examples

Input: readings collection: +-----+--------+------+ | _id | sensor | temp | +-----+--------+------+ | 1 | A | 18 | | 2 | B | 22 | | 3 | C | 30 | | 4 | D | 25 | +-----+--------+------+

Output: +-----+--------+------+ | _id | sensor | temp | +-----+--------+------+ | 2 | B | 22 | | 4 | D | 25 | +-----+--------+------+

Explanation: The query retrieves all documents from the collection that satisfy the specified filter criteria.

Complexity

Time Complexity: -

Space Complexity: -

Hints

💡 Hint 1: Use comparison operators ($gt, $gte, $lt, $lte) to filter documents based on numeric or date ranges. 💡 Hint 2: Construct the filter condition: { fieldName: { $gt: value } } inside db.<collection>.find(...). 💡 Hint 3: Chain projection or sorting if requested, and invoke .toArray() to produce the result array.

Editorial & Approach

Problem Overview & Intuition

To solve "Range Query (Between Two Values)", we query the MongoDB document store. The goal is to find all temperatures between `20` (inclusive) and `30` (exclusive) from the `readings` collection. 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.readings.find({ temp: { $gte: 20, $lt: 30 } }).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.

Range Query (Between Two Values)

Easy

Find all temperatures between 20 (inclusive) and 30 (exclusive) from the readings collection.

Example Scenarios

1Example 1

Input:

readings collection

_id	sensor	temp
1	A	18
2	B	22
3	C	30
4	D	25

Output:

_id	sensor	temp
2	B	22
4	D	25

Explanation:

The query retrieves all documents from the collection that satisfy the specified filter criteria.

MongoDB Editor

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Query Results (JSON)

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