Distance-vector routing ( DVR ) algorithm in java

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code in Java:

import java.io.*;
public class DVR 
{
 static int graph[][];
 static int via[][];
 static int rt[][];
 static int v;
 static int e;

 public static void main(String args[]) throws IOException
 {
  BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
  
  System.out.println("Please enter the number of Vertices: ");
  v = Integer.parseInt(br.readLine());
  
  System.out.println("Please enter the number of Edges: ");
  e = Integer.parseInt(br.readLine());
  
  graph = new int[v][v];
  via = new int[v][v];
  rt = new int[v][v];
  for(int i = 0; i < v; i++)
   for(int j = 0; j < v; j++)
   {
    if(i == j)
     graph[i][j] = 0;
    else
     graph[i][j] = 9999;
   }
  
  for(int i = 0; i < e; i++)
  {
   System.out.println("Please enter data for Edge " + (i + 1) + ":");
   System.out.print("Source: ");
   int s = Integer.parseInt(br.readLine());
   s--;
   System.out.print("Destination: ");
   int d = Integer.parseInt(br.readLine());
   d--;
   System.out.print("Cost: ");
   int c = Integer.parseInt(br.readLine());
   graph[s][d] = c;
   graph[d][s] = c;
  }
  
  dvr_calc_disp("The initial Routing Tables are: ");
  
  System.out.print("Please enter the Source Node for the edge whose cost has changed: ");
  int s = Integer.parseInt(br.readLine());
  s--;
  System.out.print("Please enter the Destination Node for the edge whose cost has changed: ");
  int d = Integer.parseInt(br.readLine());
  d--;
  System.out.print("Please enter the new cost: ");
  int c = Integer.parseInt(br.readLine());
  graph[s][d] = c;
  graph[d][s] = c;
  
  dvr_calc_disp("The new Routing Tables are: ");
 }
 
 static void dvr_calc_disp(String message)
 {
  System.out.println();
  init_tables();
  update_tables();
  System.out.println(message);
  print_tables();
  System.out.println();
 }
 
 static void update_table(int source)
 {
  for(int i = 0; i < v; i++)
  {
   if(graph[source][i] != 9999)
   {
    int dist = graph[source][i];
    for(int j = 0; j < v; j++)
    {
     int inter_dist = rt[i][j];
     if(via[i][j] == source)
      inter_dist = 9999;
     if(dist + inter_dist < rt[source][j])
     {
      rt[source][j] = dist + inter_dist;
      via[source][j] = i;
     }
    }
   }
  }
 }
 
 static void update_tables()
 {
  int k = 0;
  for(int i = 0; i < 4*v; i++)
  {
   update_table(k);
   k++;
   if(k == v)
    k = 0;
  }
 }
 
 static void init_tables()
 {
  for(int i = 0; i < v; i++)
  {
   for(int j = 0; j < v; j++)
   {
    if(i == j)
    {
     rt[i][j] = 0;
     via[i][j] = i;
    }
    else
    {
     rt[i][j] = 9999;
     via[i][j] = 100;
    }
   }
  }
 }
 
 static void print_tables()
 {
  for(int i = 0; i < v; i++)
  {
   for(int j = 0; j < v; j++)
   {
    System.out.print("Dist: " + rt[i][j] + "    ");
   }
   System.out.println();
  }
 }
 
}

output:-

Please enter the number of Vertices: 
4
Please enter the number of Edges: 
5
Please enter data for Edge 1:
Source: 1
Destination: 2
Cost: 1
Please enter data for Edge 2:
Source: 1
Destination: 3
Cost: 3
Please enter data for Edge 3:
Source: 2
Destination: 3
Cost: 1
Please enter data for Edge 4:
Source: 2
Destination: 4
Cost: 1
Please enter data for Edge 5:
Source: 3
Destination: 4
Cost: 4

The initial Routing Tables are: 
Dist: 0    Dist: 1    Dist: 2    Dist: 2    
Dist: 1    Dist: 0    Dist: 1    Dist: 1    
Dist: 2    Dist: 1    Dist: 0    Dist: 2    
Dist: 2    Dist: 1    Dist: 2    Dist: 0    

Please enter the Source Node for the edge whose cost has changed: 2
Please enter the Destination Node for the edge whose cost has changed: 4
Please enter the new cost: 10

The new Routing Tables are: 
Dist: 0    Dist: 1    Dist: 2    Dist: 6    
Dist: 1    Dist: 0    Dist: 1    Dist: 5    
Dist: 2    Dist: 1    Dist: 0    Dist: 4    
Dist: 6    Dist: 5    Dist: 4    Dist: 0    
--------------------------------