leetcode説明--841.Keys and Rooms

タイトル

There are N rooms and you start in room 0 . Each room has a distinct number in 0, 1, 2, ..., N-1 , and each room may have some keys to access the next room.
Formally, each room i has a list of keys rooms[i] , and each key rooms[i][j] is an integer in [0, 1, ..., N-1] where N = rooms.length . A key rooms[i][j] = v opens the room with number v .
Initially, all the rooms start locked (except for room 0 ).
You can walk back and forth between rooms freely.
Return true if and only if you can enter every room.
Example 1:

Input: [[1],[2],[3],[]]
Output: true
Explanation:  
We start in room 0, and pick up key 1.
We then go to room 1, and pick up key 2.
We then go to room 2, and pick up key 3.
We then go to room 3.  Since we were able to go to every room, we return true.

Example 2:

Input: [[1,3],[3,0,1],[2],[0]]
Output: false
Explanation: We can't enter the room with number 2.

Note:

1 <= rooms.length <= 1000
0 <= rooms[i].length <= 1000
The number of keys in all rooms combined is at most 3000.

タイトルアドレス

説明する

これは典型的な図の遍歴であり,ここでは広さ優先遍歴を採用し,広さ優先遍歴はキューというデータ構造で実現できる.アクセスしたroomを記録するためのSetも必要です.この問題は比較的に簡単だと感じます

JAvaコード

class Solution {
    public boolean canVisitAllRooms(List> rooms) {
        Set set = new HashSet();
        Queue queue = new LinkedList<>();
        for(Integer x:rooms.get(0)){
            queue.offer(x);
        }
        while(!queue.isEmpty()){
            int room = queue.poll();
            if(set.contains(room)){
                continue;
            }else{
                set.add(room);
                List list = rooms.get(room);
                if(list!=null && list.size()>0){
                    for(Integer x: list){
                        queue.offer(x);
                    }
                }
            }
        }
        for(int i=1;i