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# 0841. Keys and Rooms

<https://leetcode.com/problems/keys-and-rooms>

## Description

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**.

## ac

```java
```