graph-algorithms/Kosaraju/main.cpp

84 lines
1.9 KiB
C++
Raw Permalink Normal View History

2024-07-14 16:44:12 +02:00
// Kosarajus algorithm to find strongly connected components of a directed graph
// Authors: Georǵi Kocharyan, Maximilian Keßler
#include <iostream>
#include <cstdio>
#include <vector>
#include <stack>
2024-08-01 23:05:04 +02:00
#include "../digraph.h"
2024-07-14 16:44:12 +02:00
// push nodes in post-order
void dfs1(Digraph const & G, int n, std::vector<bool> & vis, std::stack<int> & node_order) {
if (vis[n])
{
return; //if node is already visited don't
}
vis[n] = true;
for(auto i: G.adjList(n))
{
dfs1(G, i, vis, node_order);
}
node_order.push(n);
}
//this function traverses the transpose graph
void dfs2(Digraph const & G, int n, std::vector<bool> & vis2, std::stack<int> & node_order){
if (vis2[n])
{
return; // if node is already visited
}
std::cout << n << " ";
vis2[n] = true;
for(auto i: G.adjList(n))
{
dfs2(G, i, vis2, node_order);
}
}
// print each component in seperate line, output amount
int kosaraju(Digraph const & G) {
int scc_count = 0; //keep count of strongly connected components
std::stack<int> node_order;
std::vector<bool> vis2 (G.num_nodes(), false);
std::vector<bool> vis (G.num_nodes(), false); //store node visit stat for dfs
for(int i = 0; i < G.num_nodes(); i++)
{
dfs1(G, i, vis, node_order);
}
while(!node_order.empty()) {
int node_id = node_order.top();
node_order.pop();
if (vis2[node_id] == false)
{
dfs2(G.transpose(), node_id, vis2, node_order);
scc_count++;
std::cout << std::endl;
}
}
return scc_count;
}
int main() {
int size = 10;
Digraph G(size);
G.add_edge(3,4);
G.add_edge(4,3);
G.add_edge(5,6);
G.add_edge(6,7);
G.add_edge(7,5);
G.add_edge(7,3);
G.add_edge(0,3);
G.add_edge(3,0);
int components= kosaraju(G);
std::cout<< "Components: "<< components << std::endl;
return 0;
}