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 
a = pd.read_csv('nowcoder.csv')
data = a.groupby('user_id')['date'].count()  # 按照user_id统计日期出现的次数
b = a['user_id'].count()  # user_id出现的总次数
data.to_csv('test.csv', header=False, encoding='utf-8')
data1 = pd.read_csv('test.csv', encoding='utf-8', names=['user_id', '次数'])
data2 = data1['次数'].value_counts()[2] / b  # 次数是2的个数/user_id出现的总次数
print('%.2f' % data2)  # 保留两位小数