一、题目

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.

二、题解

class Solution {
public:
    void dfs(vector<vector<int>>& rooms,vector<bool>& visited,int key){
        if(visited[key]) return;
        visited[key] = true;
        vector<int> keys = rooms[key];
        for(int i = 0;i < keys.size();i++){
            dfs(rooms,visited,keys[i]);
        }
    }
    bool canVisitAllRooms(vector<vector<int>>& rooms) {
        vector<bool> visited(rooms.size(),false);
        dfs(rooms,visited,0);
        for(int i = 0;i < visited.size();i++){
            if(visited[i] == false) return false;
        }
        return true;
    }
};