Group all payments by `method` (card, paypal, etc.), calculate the total `amount` and count per method, sort by total amount descending.

Problem Statement

<p>Group all payments by <code>method</code> (card, paypal, etc.), calculate the total <code>amount</code> and count per method, sort by total amount descending.</p>

Examples

Input: payments collection: +-----+--------+--------+ | _id | method | amount | +-----+--------+--------+ | 1 | card | 100 | | 2 | paypal | 50 | | 3 | card | 200 | | 4 | card | 150 | | 5 | paypal | 75 | +-----+--------+--------+

Output: +--------+-------------+----------+ | _id | totalAmount | txnCount | +--------+-------------+----------+ | card | 450 | 3 | | paypal | 125 | 2 | +--------+-------------+----------+

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

Complexity

Time Complexity: -

Space Complexity: -

Hints

💡 Hint 1: This problem requires grouping documents by a key and aggregating values. Use db.<collection>.aggregate([...]) with a $group stage. 💡 Hint 2: In the $group stage, set _id to the grouping field (e.g. "$category" or "$dept") and use accumulator operators like $sum, $avg, $max, or $min. 💡 Hint 3: Remember to call .toArray() at the end of the aggregation pipeline to return the resolved documents array.

Editorial & Approach

Problem Overview & Intuition

To solve "Payment Status Breakdown", we query the MongoDB document store. The goal is to group all payments by `method` (card, paypal, etc.), calculate the total `amount` and count per method, sort by total amount descending. Using an aggregation pipeline, 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 aggregation stages ($match, $group, $sort, etc.).
Resolve Cursor: Invoke .toArray() to transform the query cursor into the required array of documents.

Optimal Implementation (MongoDB)

function solve(db) {
  return db.payments.aggregate([
    { $group: { _id: "$method", totalAmount: { $sum: "$amount" }, txnCount: { $sum: 1 } } },
    { $sort: { totalAmount: -1 } }
  ]);
}

Complexity Analysis

Time Complexity O(N) pipeline traversal through aggregation stages.

Space Complexity O(M) intermediate document buffer in aggregation pipeline.

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.

Payment Status Breakdown

Hard

Group all payments by method (card, paypal, etc.), calculate the total amount and count per method, sort by total amount descending.

Example Scenarios

1Example 1

Input:

payments collection

_id	method	amount
1	card	100
2	paypal	50
3	card	200
4	card	150
5	paypal	75

Output:

_id	totalAmount	txnCount
card	450	3
paypal	125	2

Explanation:

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

MongoDB Editor

Loading Editor...

Query Results (JSON)

Run your MongoDB code to see results here.