Leetcode #1907: Count Salary Categories
In this guide, we solve Leetcode #1907 Count Salary Categories 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: Accounts +-------------+------+ | Column Name | Type | +-------------+------+ | account_id | int | | income | int | +-------------+------+ account_id is the primary key (column with unique values) for this table. Each row contains information about the monthly income for one bank account.
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 |
+-------------+------+
| account_id | int |
| income | int |
+-------------+------+
account_id is the primary key (column with unique values) for this table.
Each row contains information about the monthly income for one bank account.
Python Solution
import duckdb
import pandas as pd
def solution(accounts: pd.DataFrame) -> pd.DataFrame:
con = duckdb.connect()
con.register("Accounts", accounts)
return con.execute("""WITH
S AS (
SELECT 'Low Salary' AS category
UNION
SELECT 'Average Salary'
UNION
SELECT 'High Salary'
),
T AS (
SELECT
CASE
WHEN income < 20000 THEN "Low Salary"
WHEN income > 50000 THEN 'High Salary'
ELSE 'Average Salary'
END AS category,
COUNT(1) AS accounts_count
FROM Accounts
GROUP BY 1
)
SELECT category, IFNULL(accounts_count, 0) AS accounts_count
FROM
S
LEFT JOIN T USING (category);""").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.