LeetCode 614: Second Degree Follower Solution

Master LeetCode problem 614 (Second Degree Follower), a medium challenge, with our optimized solutions in Java, C++, and Python. Explore detailed explanations, test your code in our interactive editor, and prepare for coding interviews.

614. Second Degree Follower

Medium

Database

Problem Explanation

Explanation:

To solve this problem, we need to find the second-degree followers for each user in a social network. We can achieve this by first finding all the followers for each user, then finding the followers of those followers. Finally, we can count the second-degree followers for each user.

Algorithm:

Create a HashMap to store the followers for each user.
Populate the HashMap with the direct followers for each user.
Iterate through the direct followers for each user and find their followers.
Increment the count of second-degree followers for each user.
Return the count of second-degree followers for each user.

Time Complexity:

The time complexity of this algorithm is O(n^2), where n is the number of users in the social network.

Space Complexity:

The space complexity of this algorithm is O(n), where n is the number of users in the social network.

: :

Solution Code

class Solution {
    public List<Integer> countSecondDegreeFollowers(int[][] followRelations) {
        Map<Integer, Set<Integer>> followers = new HashMap<>();
        Map<Integer, Integer> secondDegreeFollowers = new HashMap<>();
        
        for (int[] relation : followRelations) {
            followers.putIfAbsent(relation[0], new HashSet<>());
            followers.get(relation[0]).add(relation[1]);
        }
        
        for (int user : followers.keySet()) {
            for (int follower : followers.get(user)) {
                Set<Integer> secondFollowers = followers.getOrDefault(follower, new HashSet<>());
                for (int secondFollower : secondFollowers) {
                    if (secondFollower != user && !followers.get(user).contains(secondFollower)) {
                        secondDegreeFollowers.put(secondFollower, secondDegreeFollowers.getOrDefault(secondFollower, 0) + 1);
                    }
                }
            }
        }
        
        List<Integer> result = new ArrayList<>();
        for (int user : followers.keySet()) {
            result.add(secondDegreeFollowers.getOrDefault(user, 0));
        }
        
        return result;
    }
}

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Frequently Asked Questions

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What is the time complexity of LeetCode 614 (Second Degree Follower)?

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