841

class Solution {
public:
    unordered_map<int, bool> seen;
    bool canVisitAllRooms(vector<vector<int>>& rooms) {
        stack<int> stk;
        stk.push(0);
        seen[0] = true;

        while(!stk.empty()){
            int curr = stk.top();
            stk.pop();
            for(int next: rooms[curr]){
                if(!seen.count(next)){
                    seen[next] = true;
                    stk.push(next);
                }
            }
        }
        return seen.size() == rooms.size();
    }
};