[Python/Pandas] 리트코드 1633. Percentage of Users Attended a Contest

문제

Table: Users
+-------------+---------+
| Column Name | Type    |
+-------------+---------+
| user_id     | int     |
| user_name   | varchar |
+-------------+---------+
user_id is the primary key (column with unique values) for this table.
Each row of this table contains the name and the id of a user.

Table: Register
+-------------+---------+
| Column Name | Type    |
+-------------+---------+
| contest_id  | int     |
| user_id     | int     |
+-------------+---------+
(contest_id, user_id) is the primary key (combination of columns with unique values) for this table.
Each row of this table contains the id of a user and the contest they registered into.

 

Write a solution to find the percentage of the users registered in each contest rounded to two decimals.
Return the result table ordered by percentage in descending order. In case of a tie, order it by contest_id in ascending order.

 

https://leetcode.com/problems/percentage-of-users-attended-a-contest/description/?lang=pythondata

예시

Input: 
Users table:
+---------+-----------+
| user_id | user_name |
+---------+-----------+
| 6       | Alice     |
| 2       | Bob       |
| 7       | Alex      |
+---------+-----------+
Register table:
+------------+---------+
| contest_id | user_id |
+------------+---------+
| 215        | 6       |
| 209        | 2       |
| 208        | 2       |
| 210        | 6       |
| 208        | 6       |
| 209        | 7       |
| 209        | 6       |
| 215        | 7       |
| 208        | 7       |
| 210        | 2       |
| 207        | 2       |
| 210        | 7       |
+------------+---------+
Output: 
+------------+------------+
| contest_id | percentage |
+------------+------------+
| 208        | 100.0      |
| 209        | 100.0      |
| 210        | 100.0      |
| 215        | 66.67      |
| 207        | 33.33      |
+------------+------------+
Explanation: 
All the users registered in contests 208, 209, and 210. The percentage is 100% and we sort them in the answer table by contest_id in ascending order.
Alice and Alex registered in contest 215 and the percentage is ((2/3) * 100) = 66.67%
Bob registered in contest 207 and the percentage is ((1/3) * 100) = 33.33%

문제 풀이

import pandas as pd

def users_percentage(users: pd.DataFrame, register: pd.DataFrame) -> pd.DataFrame:
    # 전체 사용자 수 구하기
    total_num = users['user_id'].nunique()
    
    # 각 contest_id 별 사용자 수 계산
    summary = register.groupby('contest_id').size().reset_index(name='user_cnt')    
    
    # contest_id 별 percentage 계산
    summary['percentage'] = summary['user_cnt'] / total_num * 100
    
    # 비율 내림차순, contest_id 오름차순 정렬 후 출력 요구 형식에 맞추어 round
    result = summary[['contest_id', 'percentage']].sort_values(by=['percentage', 'contest_id'], ascending=[False, True]).round(2)
    return result

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