//User function Template for Java

class Solution

{

    public ArrayList<ArrayList<Integer>> criticalConnections(int v, ArrayList<ArrayList<Integer>> adj)

    {

        // Code here

         return getBridges(adj, v);

    }

    public ArrayList<ArrayList<Integer>> getBridges(ArrayList<ArrayList<Integer>>adj, int v){

        int[]dt = new int[v];

        int[]low = new int[v];

        boolean[]vis = new boolean[v];

        ArrayList<ArrayList<Integer>>ans = new ArrayList<>();

        dfs(adj, vis, dt, low, 0, -1,ans);

        Collections.sort(ans, (a,b)->{

            if(a.get(0).equals(b.get(0))){

                return a.get(1)-b.get(1);

            }else{

                return a.get(0)-b.get(0);

            }

        });

        return ans;

    }

    int time = 0;

    public void dfs(ArrayList<ArrayList<Integer>>adj, boolean[]vis, int[]dt, int[]low, int curr, int parent, ArrayList<ArrayList<Integer>>ans){

        vis[curr] = true;

        dt[curr] = low[curr] = ++time;

        for(int node : adj.get(curr)){

            if(node == parent)continue;

            if(!vis[node]){

                dfs(adj, vis, dt,low, node, curr, ans);

                low[curr] = Math.min(low[curr], low[node]);

                // bridge condition

                if(low[node]>dt[curr]){

                    ArrayList<Integer>bridge = new ArrayList<>();

                    bridge.add(curr);

                    bridge.add(node);

                    Collections.sort(bridge);

                    ans.add(bridge);

                }

            }else{

                low[curr] = Math.min(low[curr], dt[node]);

            }

        }

    }

}