(3, 5)<\/li>\n<\/ul>\n\n Student 1’s friends are 2 and 3, and their friends are 4 and 5.
\n Therefore, the total number of friends of friends for student 1 is 4.\n <\/p>\n<\/section>\n\nInput Format<\/h2>\n
\nfriends: List>, target: Int<\/code>\n<\/p>\n\n – friends<\/code>: A list of tuples representing friendships,
\n – target<\/code>: The student whose friends of friends you want to find\n <\/p>\n<\/section>\n\nOutput Format<\/h2>\n
\n – An integer representing the number of friends of friends\n <\/p>\n<\/section>\n\nProblem Solving Process<\/h2>\n
\n To understand friendships, we can apply graph theory.
\n Each student becomes a node, and friendships are represented as edges.
\n This allows us to explore the given student and their friends’ friends.\n <\/p>\n
1. Constructing the Graph<\/h3>\n
\n First, we need to convert the friendships into a graph format.
\n Let’s create a map with each student as keys and their friends as values.\n <\/p>\n
\nfun buildGraph(friends: List>): Map> {\n val graph = mutableMapOf>()\n for ((a, b) in friends) {\n graph.computeIfAbsent(a) { mutableListOf() }.add(b)\n graph.computeIfAbsent(b) { mutableListOf() }.add(a)\n }\n return graph\n}\n <\/code><\/pre>\n2. Finding Friends of Friends<\/h3>\n
\n Once the graph is constructed, we need to find the friends of a specific student and
\n obtain the list of their friends’ friends.
\n Care must be taken to ensure that the friends list does not contain duplicates.\n <\/p>\n
\nfun findFriendsOfFriends(friends: List>, target: Int): Int {\n val graph = buildGraph(friends)\n val directFriends = graph[target] ?: return 0\n val friendsOfFriends = mutableSetOf()\n \n for (friend in directFriends) {\n val friendsOfCurrentFriend = graph[friend]\n if (friendsOfCurrentFriend != null) {\n for (fof in friendsOfCurrentFriend) {\n if (fof != target && !directFriends.contains(fof)) {\n friendsOfFriends.add(fof)\n }\n }\n }\n }\n return friendsOfFriends.size\n}\n <\/code><\/pre>\n3. Complete Code<\/h3>\n
Now, let’s organize the complete code.<\/p>\n
\nfun main() {\n val friendsList = listOf(Pair(1, 2), Pair(1, 3), Pair(2, 4), Pair(3, 5))\n val targetStudent = 1\n val result = findFriendsOfFriends(friendsList, targetStudent)\n println(\"Number of friends of friends for student $targetStudent: $result\")\n}\n <\/code><\/pre>\n<\/section>\n\nComplexity Analysis<\/h2>\n
\n The time complexity of this algorithm is O(N + M).
\n Here, N is the number of students, and M is the number of friendships.
\n The space complexity is also O(N + M).
\n This is because each student and friendship is stored in graph form.\n <\/p>\n<\/section>\n\nExample and Test Cases<\/h2>\n
Let’s verify that the function works correctly with various examples.<\/p>\n
\n- \nExample 1:<\/strong>
\n
Input: <\/p>\n\n friendsList = listOf(Pair(1, 2), Pair(1, 3), Pair(2, 4), Pair(3, 5))\n targetStudent = 1\n <\/code><\/pre>\n Output: “Number of friends of friends for student 1: 2”\n <\/li>\n
- \nExample 2:<\/strong>
\n
Input: <\/p>\n\n friendsList = listOf(Pair(1, 2), Pair(1, 3), Pair(2, 3))\n targetStudent = 1\n <\/code><\/pre>\n Output: “Number of friends of friends for student 1: 0”\n <\/li>\n
- \nExample 3:<\/strong>
\n
Input: <\/p>\n\n friendsList = listOf(Pair(1, 2), Pair(3, 4), Pair(4, 5))\n targetStudent = 1\n <\/code><\/pre>\n Output: “Number of friends of friends for student 1: 0”\n <\/li>\n<\/ul>\n<\/section>\n\nConclusion<\/h2>\n
\n Understanding friendship relationships is a common type of algorithm problem.
\n It can be effectively solved through graph structures,
\n and care must be taken at each step.
\n I hope this tutorial helped you learn how to solve problems using Kotlin’s features.
\n As you tackle more algorithm problems, may you continue to build your coding skills.\n <\/p>\n<\/section>\n<\/article>\n
<\/body><\/p>\n","protected":false},"excerpt":{"rendered":"
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