Leetcode #1435: Create a Session Bar Chart
In this guide, we solve Leetcode #1435 Create a Session Bar Chart 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 | +---------------------+---------+ | session_id | int | | duration | int | +---------------------+---------+ session_id is the column of unique values for this table. duration is the time in seconds that a user has visited the application.
Quick Facts
- Difficulty: Easy
- 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 |
+---------------------+---------+
| session_id | int |
| duration | int |
+---------------------+---------+
session_id is the column of unique values for this table.
duration is the time in seconds that a user has visited the application.
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("""SELECT '[0-5>' AS bin, COUNT(1) AS total FROM Sessions WHERE duration < 300
UNION
SELECT '[5-10>' AS bin, COUNT(1) AS total FROM Sessions WHERE 300 <= duration AND duration < 600
UNION
SELECT '[10-15>' AS bin, COUNT(1) AS total FROM Sessions WHERE 600 <= duration AND duration < 900
UNION
SELECT '15 or more' AS bin, COUNT(1) AS total FROM Sessions WHERE 900 <= duration;""").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.