LeetCode in Kotlin

1733. Minimum Number of People to Teach

Medium

On a social network consisting of m users and some friendships between users, two users can communicate with each other if they know a common language.

You are given an integer n, an array languages, and an array friendships where:

• There are n languages numbered 1 through n,
• languages[i] is the set of languages the ith user knows, and
• friendships[i] = [ui, vi] denotes a friendship between the users ui and vi.

You can choose one language and teach it to some users so that all friends can communicate with each other. Return the minimum number of users you need to teach.

Note that friendships are not transitive, meaning if x is a friend of y and y is a friend of z, this doesn’t guarantee that x is a friend of z.

Example 1:

Input: n = 2, languages = [[1],[2],[1,2]], friendships = [[1,2],[1,3],[2,3]]

Output: 1

Explanation: You can either teach user 1 the second language or user 2 the first language.

Example 2:

Input: n = 3, languages = [[2],[1,3],[1,2],[3]], friendships = [[1,4],[1,2],[3,4],[2,3]]

Output: 2

Explanation: Teach the third language to users 1 and 3, yielding two users to teach.

Constraints:

• 2 <= n <= 500
• languages.length == m
• 1 <= m <= 500
• 1 <= languages[i].length <= n
• 1 <= languages[i][j] <= n
• 1 <= ui < vi <= languages.length
• 1 <= friendships.length <= 500
• All tuples (ui, vi) are unique
• languages[i] contains only unique values

Solution

class Solution {
    fun minimumTeachings(n: Int, languages: Array<IntArray>, friendships: Array<IntArray>): Int {
        val m: Int = languages.size
        val speak: Array<BooleanArray> = Array(m + 1) { BooleanArray(n + 1) }
        val teach: Array<BooleanArray> = Array(m + 1) { BooleanArray(n + 1) }
        for (user in 0 until m) {
            val userLanguages: IntArray = languages[user]
            for (userLanguage: Int in userLanguages) {
                speak[user + 1][userLanguage] = true
            }
        }
        val listToTeach: MutableList<IntArray> = ArrayList()
        for (friend: IntArray in friendships) {
            val userA: Int = friend[0]
            val userB: Int = friend[1]
            var hasCommonLanguage = false
            for (language in 1..n) {
                if (speak[userA][language] && speak[userB][language]) {
                    hasCommonLanguage = true
                    break
                }
            }
            if (!hasCommonLanguage) {
                for (language in 1..n) {
                    if (!speak[userA][language]) {
                        teach[userA][language] = true
                    }
                    if (!speak[userB][language]) {
                        teach[userB][language] = true
                    }
                }
                listToTeach.add(friend)
            }
        }
        var minLanguage: Int = Int.MAX_VALUE
        var languageToTeach = 0
        for (language in 1..n) {
            var count = 0
            for (user in 1..m) {
                if (teach[user][language]) {
                    count++
                }
            }
            if (count < minLanguage) {
                minLanguage = count
                languageToTeach = language
            }
        }
        val setToTeach: MutableSet<Int> = HashSet()
        for (friend: IntArray in listToTeach) {
            val userA: Int = friend[0]
            val userB: Int = friend[1]
            if (!speak[userA][languageToTeach]) {
                setToTeach.add(userA)
            }
            if (!speak[userB][languageToTeach]) {
                setToTeach.add(userB)
            }
        }
        return setToTeach.size
    }
}

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