From 56a5b594e4b4bc2cd4071fa315089b23bce2cc66 Mon Sep 17 00:00:00 2001
From: GregorSamsa42 <geo.kochar@gmail.com>
Date: Sun, 14 Jul 2024 16:44:12 +0200
Subject: [PATCH] Kosaraju added

---
 Kosaraju/CMakeLists.txt |  6 +++
 Kosaraju/digraph.cpp    | 49 ++++++++++++++++++++++++
 Kosaraju/digraph.h      | 32 ++++++++++++++++
 Kosaraju/main.cpp       | 84 +++++++++++++++++++++++++++++++++++++++++
 4 files changed, 171 insertions(+)
 create mode 100644 Kosaraju/CMakeLists.txt
 create mode 100644 Kosaraju/digraph.cpp
 create mode 100644 Kosaraju/digraph.h
 create mode 100644 Kosaraju/main.cpp

diff --git a/Kosaraju/CMakeLists.txt b/Kosaraju/CMakeLists.txt
new file mode 100644
index 0000000..43eceba
--- /dev/null
+++ b/Kosaraju/CMakeLists.txt
@@ -0,0 +1,6 @@
+cmake_minimum_required(VERSION 3.10)
+project(Kosaraju)
+add_executable(Kosaraju
+	digraph.cpp
+	digraph.h
+	main.cpp)
\ No newline at end of file
diff --git a/Kosaraju/digraph.cpp b/Kosaraju/digraph.cpp
new file mode 100644
index 0000000..87c00d4
--- /dev/null
+++ b/Kosaraju/digraph.cpp
@@ -0,0 +1,49 @@
+#include "digraph.h"
+
+Node::Node(std::list<int> neighbours_) : neighbours(std::move(neighbours_))
+{
+
+}
+
+void Node::add_edge(int v)
+{
+  neighbours.push_back(v);
+}
+
+Digraph::Digraph(size_t num_nodes) : nodes(num_nodes)
+{
+
+}
+
+void Digraph::add_edge(int from, int to)
+{
+  nodes[from].add_edge(to);
+}
+
+std::list<int> Digraph::adjList(int node_id) const
+{
+  return (nodes[node_id]).neighbours;
+}
+
+bool Digraph::isEdge(int from, int to) const
+{
+  return (std::find(adjList(from).begin(), adjList(from).end(), to) != adjList(from).end());
+}
+
+size_t Digraph::num_nodes() const
+{
+  return nodes.size();
+}
+
+Digraph Digraph::transpose() const
+{
+  Digraph G(num_nodes());
+  for (int i = 0; i < num_nodes(); i++)
+  {
+    for (auto const& j: ((nodes[i]).neighbours))
+    {
+      G.add_edge(j,i);
+    }
+  }
+  return G;
+}
diff --git a/Kosaraju/digraph.h b/Kosaraju/digraph.h
new file mode 100644
index 0000000..e573121
--- /dev/null
+++ b/Kosaraju/digraph.h
@@ -0,0 +1,32 @@
+#ifndef C___DIGRAPH_H
+#define C___DIGRAPH_H
+
+#include <list>
+#include <vector>
+#include <algorithm>
+
+
+struct Node {
+  std::list<int> neighbours;
+
+  Node() = default;
+  Node(std::list<int> neighbours);
+  void add_edge(int v);
+};
+
+class Digraph {
+public:
+  Digraph(size_t num_nodes);
+  void add_edge(int from, int to);
+  std::list<int> adjList(int node_id) const;
+  size_t num_nodes() const;
+  Digraph transpose() const;
+  bool isEdge(int from, int to) const;
+
+private:
+  std::vector<Node> nodes;
+};
+
+#endif //C___DIGRAPH_H
+
+
diff --git a/Kosaraju/main.cpp b/Kosaraju/main.cpp
new file mode 100644
index 0000000..9574d8d
--- /dev/null
+++ b/Kosaraju/main.cpp
@@ -0,0 +1,84 @@
+//  Kosaraju’s algorithm to find strongly connected components of a directed graph
+//  Authors: Georǵi Kocharyan, Maximilian Keßler
+
+#include <iostream>
+#include <cstdio>
+#include <vector>
+#include <stack>
+
+#include "digraph.h"
+
+// 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;
+}
\ No newline at end of file