From a2bc786543c9194354dcf8d8fe5fdb241691930c Mon Sep 17 00:00:00 2001
From: GregorSamsa42 <geo.kochar@gmail.com>
Date: Wed, 24 Jul 2024 15:54:43 +0200
Subject: [PATCH] Restructured folders, added topological order alg

---
 Kosaraju/CMakeLists.txt             |  6 +--
 Kosaraju/digraph.cpp => digraph.cpp | 23 ++++++++++++
 Kosaraju/digraph.h => digraph.h     |  3 ++
 top_order/CMakeLists.txt            |  6 +++
 top_order/top_order.cpp             | 58 +++++++++++++++++++++++++++++
 5 files changed, 93 insertions(+), 3 deletions(-)
 rename Kosaraju/digraph.cpp => digraph.cpp (68%)
 rename Kosaraju/digraph.h => digraph.h (85%)
 create mode 100644 top_order/CMakeLists.txt
 create mode 100644 top_order/top_order.cpp

diff --git a/Kosaraju/CMakeLists.txt b/Kosaraju/CMakeLists.txt
index 43eceba..1cac620 100644
--- a/Kosaraju/CMakeLists.txt
+++ b/Kosaraju/CMakeLists.txt
@@ -1,6 +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
+	../digraph.cpp
+	../digraph.h
+	main.cpp)
diff --git a/Kosaraju/digraph.cpp b/digraph.cpp
similarity index 68%
rename from Kosaraju/digraph.cpp
rename to digraph.cpp
index 87c00d4..b18103e 100644
--- a/Kosaraju/digraph.cpp
+++ b/digraph.cpp
@@ -10,6 +10,11 @@ void Node::add_edge(int v)
   neighbours.push_back(v);
 }
 
+int Node::outdeg() const
+{
+  return neighbours.size();
+}
+
 Digraph::Digraph(size_t num_nodes) : nodes(num_nodes)
 {
 
@@ -30,6 +35,24 @@ bool Digraph::isEdge(int from, int to) const
   return (std::find(adjList(from).begin(), adjList(from).end(), to) != adjList(from).end());
 }
 
+int Digraph::outdeg(int node_id) const
+{
+  return nodes[node_id].outdeg();
+}
+
+std::vector<int> Digraph::indegrees() const
+{
+  std::vector<int> indegs (num_nodes(),0);
+  for(int i = 0; i < num_nodes(); i++)
+  {
+    for (auto const& j: ((nodes[i]).neighbours))
+    {
+      indegs[j]++;
+    }
+  }
+  return indegs;
+}
+
 size_t Digraph::num_nodes() const
 {
   return nodes.size();
diff --git a/Kosaraju/digraph.h b/digraph.h
similarity index 85%
rename from Kosaraju/digraph.h
rename to digraph.h
index e573121..751d89e 100644
--- a/Kosaraju/digraph.h
+++ b/digraph.h
@@ -12,6 +12,7 @@ struct Node {
   Node() = default;
   Node(std::list<int> neighbours);
   void add_edge(int v);
+  int outdeg() const;
 };
 
 class Digraph {
@@ -22,6 +23,8 @@ public:
   size_t num_nodes() const;
   Digraph transpose() const;
   bool isEdge(int from, int to) const;
+  int outdeg(int v) const;
+  std::vector<int> indegrees() const;
 
 private:
   std::vector<Node> nodes;
diff --git a/top_order/CMakeLists.txt b/top_order/CMakeLists.txt
new file mode 100644
index 0000000..dc41842
--- /dev/null
+++ b/top_order/CMakeLists.txt
@@ -0,0 +1,6 @@
+cmake_minimum_required(VERSION 3.10)
+project(top_order)
+add_executable(top_order
+	../digraph.cpp
+	../digraph.h
+	top_order.cpp)
diff --git a/top_order/top_order.cpp b/top_order/top_order.cpp
new file mode 100644
index 0000000..cfd7d33
--- /dev/null
+++ b/top_order/top_order.cpp
@@ -0,0 +1,58 @@
+//  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"
+
+
+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);
+
+    std::stack<int> zero_indegree;
+    std::vector<int> indegs = G.indegrees();
+    int amount = 0;
+
+    for(int i = 0; i < size; i++)
+    {
+            if (indegs[i] == 0)
+            {
+                zero_indegree.push(i);
+                amount++;
+            }
+    }
+
+    while(!zero_indegree.empty()) 
+    {
+        int node_id = zero_indegree.top();
+        zero_indegree.pop();
+        std::cout << node_id << ' ';
+        for(auto i: G.adjList(node_id))
+        {
+            if (indegs[i] = 1)
+            {
+                zero_indegree.push(i);
+                amount++;
+            }
+            indegs[i]--;
+        }
+    }
+    if (!(amount == size))
+    {   
+        std::cout << '\n' << "The graph contains cycles and thus has no topological order." << std::endl;
+    }
+
+    return 0;
+}
\ No newline at end of file