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.

解題

建立一個陣列紀錄拜訪過的房間。

建立一個queue存放手上的鑰匙，一開始裡面只有 0 號房的鑰匙。依序拜訪房間撿鑰匙，如果該鑰匙的房間已經被拜訪過就不要撿。

Runtime: 4 ms, faster than 91.6%

Memory Usage: 4 MB, less than 84.55%

func canVisitAllRooms(rooms [][]int) bool {
    visited := make([]bool, len(rooms))

    keys := make([]int, 0)
    keys = append(keys, 0)

    for len(keys) != 0 {
        top := keys[0]
        keys = keys[1:]

        visited[top] = true

        for _, k := range rooms[top] {
            if !visited[k] {
                keys = append(keys, k)
            }
        }
    }

    for _, v := range visited {
        if !v { return false }
    }

    return true
}