BFS of a Graph

class Solution {
  public:
    // Function to return Breadth First Traversal of given graph.
    vector<int> bfs(vector<vector<int>> &adj) {
 
        vector<int>ans; //Stores the BFS traversal order.
        queue<int>q; //Queue to process nodes in FIFO order.
        q.push(0); // Start BFS from node 0.
        unordered_map<int,bool>visited; //Keeps track of visited nodes to prevent revisiting.
        visited[0] = true; //Mark node 0 as visited.
        while(!q.empty()){
            int frontNode = q.front(); //Take the front node from the queue.
            q.pop();
            ans.push_back(frontNode);//dd the node to the result.
            
            for(auto i: adj[frontNode]){  //Traverse all adjacent nodes of frontNode.


                if(!visited[i]){
                    q.push(i); //Push it into the queue.
                    visited[i] = true; // Mark it as visited.
                }
            }
        }
        return ans;
    }
};