Leetcode #1204: Last Person to Fit in the Bus
In this guide, we solve Leetcode #1204 Last Person to Fit in the Bus 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: Queue +-------------+---------+ | Column Name | Type | +-------------+---------+ | person_id | int | | person_name | varchar | | weight | int | | turn | int | +-------------+---------+ person_id column contains unique values. This table has the information about all people waiting for a bus.
Quick Facts
- Difficulty: Medium
- Premium: No
- 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 |
+-------------+---------+
| person_id | int |
| person_name | varchar |
| weight | int |
| turn | int |
+-------------+---------+
person_id column contains unique values.
This table has the information about all people waiting for a bus.
The person_id and turn columns will contain all numbers from 1 to n, where n is the number of rows in the table.
turn determines the order of which the people will board the bus, where turn=1 denotes the first person to board and turn=n denotes the last person to board.
weight is the weight of the person in kilograms.
Python Solution
import duckdb
import pandas as pd
def solution(queue: pd.DataFrame) -> pd.DataFrame:
con = duckdb.connect()
con.register("Queue", queue)
return con.execute("""SELECT a.person_name
FROM
Queue AS a,
Queue AS b
WHERE a.turn >= b.turn
GROUP BY a.person_id
HAVING SUM(b.weight) <= 1000
ORDER BY a.turn DESC
LIMIT 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.