Leetcode #2995: Viewers Turned Streamers
In this guide, we solve Leetcode #2995 Viewers Turned Streamers 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: Sessions +---------------+----------+ | Column Name | Type | +---------------+----------+ | user_id | int | | session_start | datetime | | session_end | datetime | | session_id | int | | session_type | enum | +---------------+----------+ session_id is column of unique values for this table. session_type is an ENUM (category) type of (Viewer, Streamer).
Quick Facts
- Difficulty: Hard
- 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 |
+---------------+----------+
| user_id | int |
| session_start | datetime |
| session_end | datetime |
| session_id | int |
| session_type | enum |
+---------------+----------+
session_id is column of unique values for this table.
session_type is an ENUM (category) type of (Viewer, Streamer).
This table contains user id, session start, session end, session id and session type.
Python Solution
import duckdb
import pandas as pd
def solution(sessions: pd.DataFrame) -> pd.DataFrame:
con = duckdb.connect()
con.register("Sessions", sessions)
return con.execute("""WITH
T AS (
SELECT
user_id,
session_type,
RANK() OVER (
PARTITION BY user_id
ORDER BY session_start
) AS rk
FROM Sessions
)
SELECT user_id, COUNT(1) AS sessions_count
FROM
T AS t
JOIN Sessions AS s USING (user_id)
WHERE rk = 1 AND t.session_type = 'Viewer' AND s.session_type = 'Streamer'
GROUP BY 1
ORDER BY 2 DESC, 1 DESC;""").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.