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83 lines (79 loc) · 1.99 KB
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#include<bits/stdc++.h>
using namespace std;
void print(vector < list <int> > adjlist,int i,bool vis[])
{ //print strongly connected components
vis[i]=true;
cout<<i<<"--> ";
list<int>::iterator it;
for(it=adjlist[i].begin();it!=adjlist[i].end();it++)
{
if(!vis[*it])
print(adjlist,*it,vis);
}
cout<<endl;
}
stack <int> fillstack(vector < list <int> > adjlist,int i, stack <int> order,bool vis[])
{
vis[i]=true;
list<int>::iterator it;
for(it=adjlist[i].begin();it!=adjlist[i].end();it++)
{
if(vis[*it]==false)
fillstack(adjlist,*it,order,vis);
}
order.push(i);
//cout<<order.top()<<" ";
return order;
}
int kosaraju( vector < list <int> > adjlist, int v)
{ int count=0;
bool vis[v];
int i;
//mark all nodes as unvisited
for(i=0;i<=v;i++)
vis[i]=false;
stack <int> order;
list<int>::iterator it;
for(i=1;i<=v;i++)
{
if(vis[i]==false)
//fill stack in order of finish times using DFS
order = fillstack(adjlist,i,order,vis);
}
/*while(!order.empty())
{
cout<<order.top()<<" ";
order.pop();
}*/
for(i=1;i<=v;i++)
vis[i]=false;
for(i=0;i<v;i++)
{ //reverse the graph
for(it=adjlist[i].begin();it!=adjlist[i].end();it++)
adjlist[*it].push_back(i);
}
while(order.empty()==false)
{ //check connectivity by performing DFS on reverse graph
i= order.top();
order.pop();
if(vis[i]==false)
{//print(adjlist,i,vis);
count++;
}
}
return count;
}
int main()
{
int v,e,v1,v2,i;
cin>>v>>e;
vector < list <int> > adjlist(v+1);
for(i=0;i<e;i++)
{
cin>>v1>>v2;
adjlist[v1].push_back(v2);
adjlist[v2].push_back(v1); //for undirected graph
}
int ans=kosaraju(adjlist,v);
cout<<ans<<endl;
}