public class Solution {
    IList<IList<int>> graph;
    bool[] marked;

    public bool CanVisitAllRooms(IList<IList<int>> rooms) {
        graph = rooms;
        marked = new bool[rooms.Count];

        dfs(0);

        foreach (bool b in marked) {
            if (!b) return false;
        }

        return true;
    }

    private void dfs(int v) {
        marked[v] = true;

        foreach (int w in graph[v]) {
            if (!marked[w]) {
                dfs(w);
            }
        }
    }
}