Leetcode #2175: The Change in Global Rankings
In this guide, we solve Leetcode #2175 The Change in Global Rankings 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: TeamPoints +-------------+---------+ | Column Name | Type | +-------------+---------+ | team_id | int | | name | varchar | | points | int | +-------------+---------+ team_id contains unique values. Each row of this table contains the ID of a national team, the name of the country it represents, and the points it has in the global rankings.
Quick Facts
- Difficulty: Medium
- 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 |
+-------------+---------+
| team_id | int |
| name | varchar |
| points | int |
+-------------+---------+
team_id contains unique values.
Each row of this table contains the ID of a national team, the name of the country it represents, and the points it has in the global rankings. No two teams will represent the same country.
Python Solution
import duckdb
import pandas as pd
def solution(team_points: pd.DataFrame, points_change: pd.DataFrame) -> pd.DataFrame:
con = duckdb.connect()
con.register("TeamPoints", team_points)
con.register("PointsChange", points_change)
return con.execute("""WITH
P AS (
SELECT team_id, SUM(points_change) AS delta
FROM PointsChange
GROUP BY team_id
)
SELECT
team_id,
name,
CAST(RANK() OVER (ORDER BY points DESC, name) AS SIGNED) - CAST(
RANK() OVER (ORDER BY (points + delta) DESC, name) AS SIGNED
) AS 'rank_diff'
FROM
TeamPoints
JOIN P USING (team_id);""").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.