Timestamping the DFS - c++

Question

#include <iostream>
#include <vector>
#include <list>
using namespace std ;
class Graph
{
public:
Graph(int V)
{
this->V = V ;
G.resize(V) ;
}
void addEdge(int v , int w)
{
G[v].push_back(w) ;
G[w].push_back(v) ;
}
void DFS( int s )
{
bool *visited = new bool[this->V] ;
for( int i = 0 ; i < this->V ; i++ )
visited[i] = false ;
int *arrival = new int[this->V] ;
int *departure = new int[this->V] ;
static int t = 0 ;
DFSUtil(s,visited,arrival,departure,t) ; // Utility function to do the DFS
cout << "\n" ;
for( int i = 0 ; i < this->V ; i++ )
cout << arrival[i] << "/" << departure[i] << " " ;
}
void printGraph()
{
vector< list<int> >::iterator i ;
list<int>::iterator j ;
int k = 0 ;
int t = 0 ;
for( i = G.begin() ; i != G.end() ; ++i )
{
cout << "Node " << k++ << "->" ;
for( j = G[t].begin() ; j != G[t].end() ; ++j )
cout << *j << "->" ;
cout << "NULL\n" ;
t++ ;
}
}
private:
int V ; // number of vertices
vector< list<int> > G ; // array of lists
void DFSUtil( int s , bool *visited , int *arrival , int *departure , int t ) // Utility function to do DFS
{
cout << s << " " ;
visited[s] = true ;
arrival[s] = ++t ;
list<int>::iterator i ;
for( i = G[s].begin() ; i != G[s].end() ; ++i )
{
if( !visited[*i] )
DFSUtil(*i,visited,arrival,departure,t) ;
}
departure[s] = ++t ;
}
};
int main()
{
// Create a graph given in the above diagram
Graph g(6);
g.addEdge(0, 1);
g.addEdge(0, 2);
g.addEdge(1, 2);
g.addEdge(0, 4);
g.addEdge(0, 3);
g.addEdge(1, 4);
g.addEdge(1, 5);
g.addEdge(4, 5);
g.addEdge(3, 5);
g.printGraph() ;
cout << "Following is Depth First Traversal (starting from vertex 0) \n";
g.DFS(0);
return 0;
}
I wanted to timestamp the process of DFS ie when the search process reaches a particular node and then bactracks from it . What I mean is that when DFS begins it first visits node 0 so arrival[0] = 1 , then it recursively calls on node 1 so arrival[1] = 2 , then recursively calls on node 2 so arrival[2] = 3 , now node 2 can't call on anyone so departure[2] should be 4 and subsequently , but what my program outputs is not on the same lines as I was expecting . I thought declaring timestamp variable t as static would do the trick , but it's not working . How to correct it ?

Answer 1

"static" in this context essentially means "there is only one of these that is shared by all invokations of this function".
You're still passing a copy of the variable as a parameter to the other functions.
If you want a called function to be able to modify a variable, you pass it a reference to that variable.
Remove the "static", and change DFSUtil to
void DFSUtil(int s, bool *visited, int *arrival, int *departure, int &t)