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graph/kosaraju.cpp
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@@ -1,134 +1,135 @@
/* Implementation of Kosaraju's Algorithm to find out the strongly connected components (SCCs) in a graph.
Author:Anirban166
*/
/* Implementation of Kosaraju's Algorithm to find out the strongly connected
components (SCCs) in a graph. Author:Anirban166
*/
#include<iostream>
#include<vector>
#include <iostream>
#include <vector>
using namespace std;
/**
* Iterative function/method to print graph:
* @param a[] : array of vectors (2D)
* @param V : vertices
* @return void
**/
void print(vector<int> a[],int V)
* Iterative function/method to print graph:
* @param a[] : array of vectors (2D)
* @param V : vertices
* @return void
**/
void print(vector<int> a[], int V)
{
for(int i=0;i<V;i++)
for (int i = 0; i < V; i++)
{
if(!a[i].empty())
cout<<"i="<<i<<"-->";
for(int j=0;j<a[i].size();j++)
cout<<a[i][j]<<" ";
if(!a[i].empty())
cout<<endl;
if (!a[i].empty())
cout << "i=" << i << "-->";
for (int j = 0; j < a[i].size(); j++) cout << a[i][j] << " ";
if (!a[i].empty())
cout << endl;
}
}
/**
* //Recursive function/method to push vertices into stack passed as parameter:
* @param v : vertices
* @param &st : stack passed by reference
* @param vis[] : array to keep track of visited nodes (boolean type)
* @param adj[] : array of vectors to represent graph
* @return void
**/
void push_vertex(int v,stack<int> &st,bool vis[],vector<int> adj[])
* //Recursive function/method to push vertices into stack passed as parameter:
* @param v : vertices
* @param &st : stack passed by reference
* @param vis[] : array to keep track of visited nodes (boolean type)
* @param adj[] : array of vectors to represent graph
* @return void
**/
void push_vertex(int v, stack<int> &st, bool vis[], vector<int> adj[])
{
vis[v]=true;
for(auto i=adj[v].begin();i!=adj[v].end();i++)
vis[v] = true;
for (auto i = adj[v].begin(); i != adj[v].end(); i++)
{
if(vis[*i]==false)
push_vertex(*i,st,vis,adj);
if (vis[*i] == false)
push_vertex(*i, st, vis, adj);
}
st.push(v);
}
/**
* //Recursive function/method to implement depth first traversal(dfs):
* @param v : vertices
* @param vis[] : array to keep track of visited nodes (boolean type)
* @param grev[] : graph with reversed edges
* @return void
**/
void dfs(int v,bool vis[],vector<int> grev[])
* //Recursive function/method to implement depth first traversal(dfs):
* @param v : vertices
* @param vis[] : array to keep track of visited nodes (boolean type)
* @param grev[] : graph with reversed edges
* @return void
**/
void dfs(int v, bool vis[], vector<int> grev[])
{
vis[v]=true;
vis[v] = true;
// cout<<v<<" ";
for(auto i=grev[v].begin();i!=grev[v].end();i++)
for (auto i = grev[v].begin(); i != grev[v].end(); i++)
{
if(vis[*i]==false)
dfs(*i,vis,grev);
if (vis[*i] == false)
dfs(*i, vis, grev);
}
}
//function/method to implement Kosaraju's Algorithm:
// function/method to implement Kosaraju's Algorithm:
/**
* Info about the method
* @param V : vertices in graph
* @param adj[] : array of vectors that represent a graph (adjacency list/array)
* @return int ( 0, 1, 2..and so on, only unsigned values as either there can be no SCCs i.e. none(0) or there will be x no. of SCCs (x>0))
i.e. it returns the count of (number of) strongly connected components (SCCs) in the graph. (variable 'count_scc' within function)
* @return int ( 0, 1, 2..and so on, only unsigned values as either there can be
no SCCs i.e. none(0) or there will be x no. of SCCs (x>0)) i.e. it returns the
count of (number of) strongly connected components (SCCs) in the graph.
(variable 'count_scc' within function)
**/
int kosaraju(int V, vector<int> adj[])
{
bool vis[V]={};
bool vis[V] = {};
stack<int> st;
for(int v=0;v<V;v++)
for (int v = 0; v < V; v++)
{
if(vis[v]==false)
push_vertex(v,st,vis,adj);
if (vis[v] == false)
push_vertex(v, st, vis, adj);
}
//making new graph (grev) with reverse edges as in adj[]:
// making new graph (grev) with reverse edges as in adj[]:
vector<int> grev[V];
for(int i=0;i<V+1;i++)
for (int i = 0; i < V + 1; i++)
{
for(auto j=adj[i].begin();j!=adj[i].end();j++)
for (auto j = adj[i].begin(); j != adj[i].end(); j++)
{
grev[*j].push_back(i);
}
}
// cout<<"grev="<<endl; ->debug statement
// print(grev,V); ->debug statement
//reinitialise visited to 0
for(int i=0;i<V;i++)
vis[i]=false;
int count_scc=0;
while(!st.empty())
// reinitialise visited to 0
for (int i = 0; i < V; i++) vis[i] = false;
int count_scc = 0;
while (!st.empty())
{
int t=st.top();
int t = st.top();
st.pop();
if(vis[t]==false)
if (vis[t] == false)
{
dfs(t,vis,grev);
dfs(t, vis, grev);
count_scc++;
}
}
// cout<<"count_scc="<<count_scc<<endl; //in case you want to print here itself, uncomment & change return type of function to void.
// cout<<"count_scc="<<count_scc<<endl; //in case you want to print here
// itself, uncomment & change return type of function to void.
return count_scc;
}
//All critical/corner cases have been taken care of.
//Input your required values: (not hardcoded)
// All critical/corner cases have been taken care of.
// Input your required values: (not hardcoded)
int main()
{
int t;
cin>>t;
while(t--)
cin >> t;
while (t--)
{
int a,b ; //a->number of nodes, b->directed edges.
cin>>a>>b;
int m,n;
vector<int> adj[a+1];
for(int i=0;i<b;i++) //take total b inputs of 2 vertices each required to form an edge.
int a, b; // a->number of nodes, b->directed edges.
cin >> a >> b;
int m, n;
vector<int> adj[a + 1];
for (int i = 0; i < b; i++) // take total b inputs of 2 vertices each
// required to form an edge.
{
cin>>m>>n; //take input m,n denoting edge from m->n.
cin >> m >> n; // take input m,n denoting edge from m->n.
adj[m].push_back(n);
}
//pass number of nodes and adjacency array as parameters to function:
cout<<kosaraju(a, adj)<<endl;
// pass number of nodes and adjacency array as parameters to function:
cout << kosaraju(a, adj) << endl;
}
return 0;
}