Leetcode #2020: Number of Accounts That Did Not Stream
In this guide, we solve Leetcode #2020 Number of Accounts That Did Not Stream in Python and focus on the core idea that makes the solution efficient.
You will see the intuition, the step-by-step method, and a clean Python implementation you can use in interviews.
Problem Statement
Table: Subscriptions +-------------+------+ | Column Name | Type | +-------------+------+ | account_id | int | | start_date | date | | end_date | date | +-------------+------+ account_id is the primary key column for this table. Each row of this table indicates the start and end dates of an account's subscription.
Quick Facts
- Difficulty: Medium
- Premium: Yes
- Tags: Database
Intuition
The task is relational in nature, which maps cleanly to DataFrame operations in Python.
By treating tables as DataFrames, joins and group-bys become concise and readable.
Approach
Load the inputs as DataFrames and apply the appropriate merge, filter, or group-by.
Select or rename the columns to match the required output.
Steps:
- Load inputs as DataFrames.
- Apply merge/groupby/filter operations.
- Select the output columns.
Example
+-------------+------+
| Column Name | Type |
+-------------+------+
| account_id | int |
| start_date | date |
| end_date | date |
+-------------+------+
account_id is the primary key column for this table.
Each row of this table indicates the start and end dates of an account's subscription.
Note that always start_date < end_date.
Python Solution
import duckdb
import pandas as pd
def solution(subscriptions: pd.DataFrame, streams: pd.DataFrame) -> pd.DataFrame:
con = duckdb.connect()
con.register("Subscriptions", subscriptions)
con.register("Streams", streams)
return con.execute("""SELECT COUNT(sub.account_id) AS accounts_count
FROM
Subscriptions AS sub
LEFT JOIN Streams USING (account_id)
WHERE
YEAR(start_date) <= 2021
AND YEAR(end_date) >= 2021
AND (YEAR(stream_date) != 2021 OR stream_date > end_date);""").df()
Complexity
The time complexity is O(n log n) (typical). The space complexity is O(n).
Edge Cases and Pitfalls
Watch for boundary values, empty inputs, and duplicate values where applicable. If the problem involves ordering or constraints, confirm the invariant is preserved at every step.
Summary
This Python solution focuses on the essential structure of the problem and keeps the implementation interview-friendly while meeting the constraints.