Input:
Graph(directed and undirected)

Objective:
Finding Mother Vertex. 

Approach:
Simple approach using DFS, more time complexity. This helps just to understand DFS better.
Implemented using java.

package dfs;
import java.io.*;
import java.util.*;


public class Graph {

int V;
LinkedList<Integer> adj[];

Graph(int V)
{
this.V = V;
adj = new LinkedList[V];
for(int i=0;i<V;i++)
adj[i] = new LinkedList();
}

void addEdge(int u,int v)
{
adj[u].add(v);
}

void DFS_Util(boolean visited[], int s)
{
visited[s] = true;
// System.out.println(s+" ");

Iterator<Integer> i = adj[s].listIterator();
while(i.hasNext())
{
int n = i.next();
if(!visited[n])
DFS_Util(visited,n);
}
}

int DFS(int s)
{
int ans = 0;
boolean visited[] = new boolean[V];
DFS_Util(visited,s);
for(int i=0;i<V;i++)
{
if(visited[i] == false)
ans=0;
else
ans=1;
}
return ans;
}


public static void main(String args[])
    {
        Graph g = new Graph(7);
       
        g.addEdge(0, 1);
        g.addEdge(0, 2);
        g.addEdge(1, 3);
        g.addEdge(4, 1);
        g.addEdge(6, 4);
        g.addEdge(5, 6);
        g.addEdge(5, 2);
        g.addEdge(6, 0);
     
        for(int i=0;i<7;i++)
        {
        if(g.DFS(i) != 1)
        continue;
        else
        {
        System.out.println(i);
        break;
        }
        }
    }


}