Leetcode #1645: Hopper Company Queries II
In this guide, we solve Leetcode #1645 Hopper Company Queries II 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: Drivers +-------------+---------+ | Column Name | Type | +-------------+---------+ | driver_id | int | | join_date | date | +-------------+---------+ driver_id is the column with unique values for this table. Each row of this table contains the driver's ID and the date they joined the Hopper company.
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 |
+-------------+---------+
| driver_id | int |
| join_date | date |
+-------------+---------+
driver_id is the column with unique values for this table.
Each row of this table contains the driver's ID and the date they joined the Hopper company.
Python Solution
import duckdb
import pandas as pd
def solution(drivers: pd.DataFrame, rides: pd.DataFrame, accepted_rides: pd.DataFrame) -> pd.DataFrame:
con = duckdb.connect()
con.register("Drivers", drivers)
con.register("Rides", rides)
con.register("AcceptedRides", accepted_rides)
return con.execute("""WITH RECURSIVE
Month AS (
SELECT 1 AS month
UNION
SELECT month + 1
FROM Month
WHERE month < 12
),
S AS (
SELECT month, driver_id, join_date
FROM
Month AS m
LEFT JOIN Drivers AS d
ON YEAR(d.join_date) < 2020
OR (YEAR(d.join_date) = 2020 AND MONTH(d.join_date) <= month)
),
T AS (
SELECT driver_id, requested_at
FROM
Rides
JOIN AcceptedRides USING (ride_id)
WHERE YEAR(requested_at) = 2020
)
SELECT
month,
IFNULL(
ROUND(COUNT(DISTINCT t.driver_id) * 100 / COUNT(DISTINCT s.driver_id), 2),
0
) AS working_percentage
FROM
S AS s
LEFT JOIN T AS t
ON s.driver_id = t.driver_id
AND s.join_date <= t.requested_at
AND s.month = MONTH(t.requested_at)
GROUP BY 1;""").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.