1917. Leetcodify Friends Recommendations π
Description
Table: Listens
+-------------+---------+ | Column Name | Type | +-------------+---------+ | user_id | int | | song_id | int | | day | date | +-------------+---------+ This table may contain duplicates (In other words, there is no primary key for this table in SQL). Each row of this table indicates that the user user_id listened to the song song_id on the day day.
Table: Friendship
+---------------+---------+ | Column Name | Type | +---------------+---------+ | user1_id | int | | user2_id | int | +---------------+---------+ In SQL,(user1_id, user2_id) is the primary key for this table. Each row of this table indicates that the users user1_id and user2_id are friends. Note that user1_id < user2_id.
Recommend friends to Leetcodify users. We recommend user x
to user y
if:
- Users
x
andy
are not friends, and - Users
x
andy
listened to the same three or more different songs on the same day.
Note that friend recommendations are unidirectional, meaning if user x
and user y
should be recommended to each other, the result table should have both user x
recommended to user y
and user y
recommended to user x
. Also, note that the result table should not contain duplicates (i.e., user y
should not be recommended to user x
multiple times.).
Return the result table in any order.
The result format is in the following example.
Example 1:
Input: Listens table: +---------+---------+------------+ | user_id | song_id | day | +---------+---------+------------+ | 1 | 10 | 2021-03-15 | | 1 | 11 | 2021-03-15 | | 1 | 12 | 2021-03-15 | | 2 | 10 | 2021-03-15 | | 2 | 11 | 2021-03-15 | | 2 | 12 | 2021-03-15 | | 3 | 10 | 2021-03-15 | | 3 | 11 | 2021-03-15 | | 3 | 12 | 2021-03-15 | | 4 | 10 | 2021-03-15 | | 4 | 11 | 2021-03-15 | | 4 | 13 | 2021-03-15 | | 5 | 10 | 2021-03-16 | | 5 | 11 | 2021-03-16 | | 5 | 12 | 2021-03-16 | +---------+---------+------------+ Friendship table: +----------+----------+ | user1_id | user2_id | +----------+----------+ | 1 | 2 | +----------+----------+ Output: +---------+----------------+ | user_id | recommended_id | +---------+----------------+ | 1 | 3 | | 2 | 3 | | 3 | 1 | | 3 | 2 | +---------+----------------+ Explanation: Users 1 and 2 listened to songs 10, 11, and 12 on the same day, but they are already friends. Users 1 and 3 listened to songs 10, 11, and 12 on the same day. Since they are not friends, we recommend them to each other. Users 1 and 4 did not listen to the same three songs. Users 1 and 5 listened to songs 10, 11, and 12, but on different days. Similarly, we can see that users 2 and 3 listened to songs 10, 11, and 12 on the same day and are not friends, so we recommend them to each other.
Solutions
Solution 1
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