题解 | #牛客网用户练习的平均次日留存率#

import sys

for line in sys.stdin:
    a = line.split()
    print(int(a[0]) + int(a[1]))

import pandas as pd
df = pd.read_csv('nowcoder.csv')
df['date'] = pd.to_datetime(df['date'], format='%Y/%m/%d %H:%M')
df['date'] = df['date'].dt.date
# 只提取出user_id&date来进行识别
df1 = df[['user_id', 'date']]
df2 = df1.copy()
# 改变日期，便于根据日期和id进行匹配
df2['date'] = df2['date']-pd.Timedelta(days=1)
df1_1 = df1.groupby(['date'])['user_id'].count().reset_index()
rename_columns_1 = {'user_id': 'user_num_today'}
df1_1.rename(columns=rename_columns_1, inplace=True)
merged_df = df1.merge(df2, how='inner', on=['user_id', 'date'])
df2 = merged_df.groupby('date')['user_id'].count().reset_index()
rename_columns_2 = {'user_id': 'user_num_tomorrow'}
df2.rename(columns=rename_columns_2, inplace=True)
merged_df1 = df1_1.merge(df2, how='left', on='date')
print(round(merged_df1['user_num_tomorrow'].sum()/merged_df1['user_num_today'].sum(), 2))