Twitter Online Assessment (OA) 2021 | Social Network

In a social media website (which is probably Twitter, if you are wondering), there are a total of n users. Each user can follow any number of other users. Let f be a matrix of relationship between these users, where f[i][j] is either 0 or 1. A 1 indicates that person i (starting from 0) is following person j, while 0 means otherwise.

In this question, we assume that each person is following themselves, and following is symmetrical. That is, if i follows j, then j follows i. We can then define a "group" of people. A "group" of people are people that follow each other, either directly or indirectly. For example, if user 0 follows user 1, and user 1 follows user 2, user 0 follows 2 indirectly.

Question: How many groups are among these n people?


  • f: An integer matrix representing the relationship matrix between the users.


  • An integer representing the number of groups among these people.


Example 1:


1f = [
2    [1, 1, 0],
3    [1, 1, 0],
4    [0, 0, 1],

Output: 2

Explanation: There are 2 groups: User 0, 1 and user 2. User 0 and 1 are in a group because they follow each other.


  • 1 <= n <= 300

Try it yourself




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