LeetCode in Kotlin

841. Keys and Rooms

Medium

There are n rooms labeled from 0 to n - 1 and all the rooms are locked except for room 0. Your goal is to visit all the rooms. However, you cannot enter a locked room without having its key.

When you visit a room, you may find a set of distinct keys in it. Each key has a number on it, denoting which room it unlocks, and you can take all of them with you to unlock the other rooms.

Given an array rooms where rooms[i] is the set of keys that you can obtain if you visited room i, return true if you can visit all the rooms, or false otherwise.

Example 1:

Input: rooms = [[1],[2],[3],[]]

Output: true

Explanation:

We visit room 0 and pick up key 1.

We then visit room 1 and pick up key 2.

We then visit room 2 and pick up key 3.

We then visit room 3.

Since we were able to visit every room, we return true.

Example 2:

Input: rooms = [[1,3],[3,0,1],[2],[0]]

Output: false

Explanation: We can not enter room number 2 since the only key that unlocks it is in that room.

Constraints:

• n == rooms.length
• 2 <= n <= 1000
• 0 <= rooms[i].length <= 1000
• 1 <= sum(rooms[i].length) <= 3000
• 0 <= rooms[i][j] < n
• All the values of rooms[i] are unique.

Solution

import java.util.TreeSet

class Solution {
    fun canVisitAllRooms(rooms: List<List<Int>?>): Boolean {
        val visited: MutableSet<Int> = HashSet()
        visited.add(0)
        val treeSet = TreeSet(rooms[0])
        while (treeSet.isNotEmpty()) {
            val key = treeSet.pollFirst()
            if (!visited.add(key)) {
                continue
            }
            if (visited.size == rooms.size) {
                return true
            }
            treeSet.addAll(rooms[key]!!)
        }
        return visited.size == rooms.size
    }
}

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