Leetcode #1919: Leetcodify Similar Friends
In this guide, we solve Leetcode #1919 Leetcodify Similar Friends 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: Listens +-------------+---------+ | Column Name | Type | +-------------+---------+ | user_id | int | | song_id | int | | day | date | +-------------+---------+ This table may contain duplicate rows. Each row of this table indicates that the user user_id listened to the song song_id on the day day.
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 |
| song_id | int |
| day | date |
+-------------+---------+
This table may contain duplicate rows.
Each row of this table indicates that the user user_id listened to the song song_id on the day day.
Python Solution
import duckdb
import pandas as pd
def solution(listens: pd.DataFrame, friendship: pd.DataFrame) -> pd.DataFrame:
con = duckdb.connect()
con.register("Listens", listens)
con.register("Friendship", friendship)
return con.execute("""SELECT DISTINCT user1_id, user2_id
FROM
Friendship AS f
LEFT JOIN Listens AS l1 ON user1_id = l1.user_id
LEFT JOIN Listens AS l2 ON user2_id = l2.user_id
WHERE l1.song_id = l2.song_id AND l1.day = l2.day
GROUP BY 1, 2, l1.day
HAVING COUNT(DISTINCT l1.song_id) >= 3;""").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.