LeetCode-in-Java

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.HashSet;
import java.util.List;
import java.util.Set;
import java.util.TreeSet;

public class Solution {
    public boolean canVisitAllRooms(List<List<Integer>> rooms) {
        Set<Integer> visited = new HashSet<>();
        visited.add(0);
        TreeSet<Integer> treeSet = new TreeSet<>(rooms.get(0));
        while (!treeSet.isEmpty()) {
            Integer key = treeSet.pollFirst();
            if (!visited.add(key)) {
                continue;
            }
            if (visited.size() == rooms.size()) {
                return true;
            }
            treeSet.addAll(rooms.get(key));
        }
        return visited.size() == rooms.size();
    }
}

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