LeetCode in Kotlin

1319. Number of Operations to Make Network Connected

Medium

There are n computers numbered from 0 to n - 1 connected by ethernet cables connections forming a network where connections[i] = [a_i, b_i] represents a connection between computers a_i and b_i. Any computer can reach any other computer directly or indirectly through the network.

You are given an initial computer network connections. You can extract certain cables between two directly connected computers, and place them between any pair of disconnected computers to make them directly connected.

Return the minimum number of times you need to do this in order to make all the computers connected. If it is not possible, return -1.

Example 1:

Input: n = 4, connections = [[0,1],[0,2],[1,2]]

Output: 1

Explanation: Remove cable between computer 1 and 2 and place between computers 1 and 3.

Example 2:

Input: n = 6, connections = [[0,1],[0,2],[0,3],[1,2],[1,3]]

Output: 2

Example 3:

Input: n = 6, connections = [[0,1],[0,2],[0,3],[1,2]]

Output: -1

Explanation: There are not enough cables.

Constraints:

1 <= n <= 10⁵
1 <= connections.length <= min(n * (n - 1) / 2, 10⁵)
connections[i].length == 2
0 <= a_i, b_i < n
a_i != b_i
There are no repeated connections.
No two computers are connected by more than one cable.

Solution

class Solution {
    private var disconnectedComputers = 0
    private lateinit var parent: IntArray
    private lateinit var rank: IntArray

    fun makeConnected(totalNumberOfComputers: Int, connections: Array<IntArray>): Int {
        if (connections.size < totalNumberOfComputers - 1) {
            return IMPOSSIBLE_TO_CONNECT
        }
        disconnectedComputers = totalNumberOfComputers
        rank = IntArray(totalNumberOfComputers)
        parent = IntArray(totalNumberOfComputers) { it }
        for (connection in connections) {
            unionFind(connection[0], connection[1])
        }
        return disconnectedComputers - 1
    }

    private fun unionFind(first: Int, second: Int) {
        val parentFirst = findParent(first)
        val parentSecond = findParent(second)
        if (parentFirst != parentSecond) {
            joinByRank(parentFirst, parentSecond)
            disconnectedComputers--
        }
    }

    private fun findParent(index: Int): Int {
        if (parent[index] != index) {
            parent[index] = findParent(parent[index])
        }
        return parent[index]
    }

    private fun joinByRank(first: Int, second: Int) {
        if (rank[first] < rank[second]) {
            parent[first] = second
        } else if (rank[second] < rank[first]) {
            parent[second] = first
        } else {
            parent[first] = second
            rank[second]++
        }
    }

    companion object {
        private const val IMPOSSIBLE_TO_CONNECT = -1
    }
}

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