Leetcode #1294: Weather Type in Each Country
In this guide, we solve Leetcode #1294 Weather Type in Each Country 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: Countries +---------------+---------+ | Column Name | Type | +---------------+---------+ | country_id | int | | country_name | varchar | +---------------+---------+ country_id is the primary key (column with unique values) for this table. Each row of this table contains the ID and the name of one country.
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 |
+---------------+---------+
| country_id | int |
| country_name | varchar |
+---------------+---------+
country_id is the primary key (column with unique values) for this table.
Each row of this table contains the ID and the name of one country.
Python Solution
import duckdb
import pandas as pd
def solution(countries: pd.DataFrame, weather: pd.DataFrame) -> pd.DataFrame:
con = duckdb.connect()
con.register("Countries", countries)
con.register("Weather", weather)
return con.execute("""SELECT
country_name,
CASE
WHEN AVG(weather_state) <= 15 THEN 'Cold'
WHEN AVG(weather_state) >= 25 THEN 'Hot'
ELSE 'Warm'
END AS weather_type
FROM
Weather AS w
JOIN Countries USING (country_id)
WHERE DATE_FORMAT(day, '%Y-%m') = '2019-11'
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.