Friend Requests II: Who Has the Most Friends
Similar Problems:
In social network like Facebook or Twitter, people send friend requests and accept others’ requests as well.
Table request_accepted holds the data of friend acceptance, while requester_id and accepter_id both are the id of a person.
| requester_id | accepter_id | accept_date| |--------------|-------------|------------| | 1 | 2 | 2016_06-03 | | 1 | 3 | 2016-06-08 | | 2 | 3 | 2016-06-08 | | 3 | 4 | 2016-06-09 |
Write a query to find the the people who has most friends and the most friends number. For the sample data above, the result is:
| id | num | |----|-----| | 3 | 3 |
Note:
- It is guaranteed there is only 1 people having the most friends.
- The friend request could only been accepted once, which mean there is no multiple records with the same requester_id and accepter_id value.
Explanation:
The person with id ‘3’ is a friend of people ‘1’, ‘2’ and ‘4’, so he has 3 friends in total, which is the most number than any others.
Follow-up:
In the real world, multiple people could have the same most number of friends, can you find all these people in this case?
Github: code.dennyzhang.com
Credits To: leetcode.com
Leave me comments, if you have better ways to solve.
## Blog link: https://code.dennyzhang.com/friend-requests-ii-who-has-the-most-friends select t.id, sum(t.num) as num from ( (select requester_id as id, count(1) as num from request_accepted group by requester_id) union all (select accepter_id as id, count(1) as num from request_accepted group by accepter_id)) as t group by t.id order by num desc limit 1
