841.CanVisitAllRooms.cs

// 841. Keys and Rooms
// 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.

public class Solution {
    int[] visited;
    public bool CanVisitAllRooms(IList<IList<int>> rooms) {
        visited = new int[rooms.Count];
        VisitRoom(rooms,0);
        visited[0] = 1;
        return rooms.Count == visited.Sum();
    }
    public void VisitRoom(IList<IList<int>> rooms, int currRoom){
        if(visited[currRoom] == 1 || visited[currRoom] == 2)
            return;
        visited[currRoom] = 2;
        foreach(int key in rooms[currRoom]){
            VisitRoom(rooms,key);
        }
        visited[currRoom] = 1;
    }
}