Merge pull request #54 from Debashis08/feature-graph-implementation

feature-test: kahn topo sort added

Author: Debashis08

Headers/0003_Graph/0003_TopologicalSort.h

@@ -17,6 +17,7 @@ namespace TopologicalSort
         int color;
         int discoveryTime;
         int finishingTime;
+        int inDegree;
         Node* parent;
         Node(int value);
     };
@@ -35,6 +36,7 @@ namespace TopologicalSort
         void PushDirectedEdge(int valueU, int valueV);
         void PushSingleNode(int valueU);
         void TopologicalSort();
+        void KahnTopologicalSort();
         vector<pair<int, pair<int, int>>> ShowTopologicalSortResult();
     };
 }

SourceCodes/0003_Graph/0003_TopologicalSort.cc

@@ -1,5 +1,6 @@
 #include "../Headers/0003_Graph/0003_TopologicalSort.h"
 #include<vector>
+#include<queue>
 #include<utility>
 #include<climits>
 #include<stdexcept>
@@ -10,9 +11,10 @@ namespace TopologicalSort
 	Node::Node(int value)
 	{
 		this->data = value;
+		this->color = WHITE;
 		this->discoveryTime = INT_MAX;
 		this->finishingTime = INT_MAX;
-		this->color = WHITE;
+		this->inDegree = 0;
 		this->parent = nullptr;
 	}
 
@@ -61,6 +63,7 @@ namespace TopologicalSort
 		Node* nodeV = this->MakeOrFindNode(valueV);
 
 		this->_adjlist[nodeU].push_back(nodeV);
+		nodeV->inDegree++;
 	}
 
 	void Graph::PushSingleNode(int valueU)
@@ -84,6 +87,53 @@ namespace TopologicalSort
 		}
 	}
 
+	void Graph::KahnTopologicalSort()
+	{
+		// Step-1 Compute in-degree of each vertices
+		// This is already done while creating the graph
+		this->time = 0;
+		queue<Node*> nodeQueue;
+
+		// Step-2 Enqueue vertices with in-degree 0
+		for (auto& node : this->_nodeMap)
+		{
+			if (node.second->inDegree == 0)
+			{
+				this->time++;
+				node.second->discoveryTime = time;
+				nodeQueue.push(node.second);
+			}
+		}
+
+		// Step-3 Process vertices in queue
+		while (!nodeQueue.empty())
+		{
+			Node* node = nodeQueue.front();
+			nodeQueue.pop();
+			this->time++;
+			node->finishingTime = time;
+			this->_topologicalSortedNodeList.push_back(node);
+			
+		// Step-4 Process all the neighbours of current node based on in-degree
+			for (auto& neighbour : this->_adjlist[node])
+			{
+				neighbour->inDegree--;
+				if (neighbour->inDegree == 0)
+				{
+					this->time++;
+					neighbour->discoveryTime = time;
+					nodeQueue.push(neighbour);
+				}
+			}
+		}
+
+		// Step-5 Check if a cycle exists
+		if (this->_topologicalSortedNodeList.size() != this->_nodeMap.size())
+		{
+			this->hasCycle = true;
+		}
+	}
+
 	vector<pair<int, pair<int, int>>> Graph::ShowTopologicalSortResult()
 	{
 		if (this->hasCycle == true)

SourceCodes/0003_Graph/0014_AllPairsShortestPathsJohnson.cc

@@ -141,8 +141,12 @@ namespace AllPairsShortestPathsJohnson
 		// Creating the graph G'
 		this->_augmentedAdjlist = this->_adjlist;
 		this->_augmentedEdgeList = this->_edgeList;
+
+		// Source Node s
 		Node* source = new Node(0);
 		this->_nodeMap[0] = source;
+
+		// Creating all the augmented edges in G'.E = G.E U {(s, v) : v in G.V
 		for (auto& node : this->_nodeMap)
 		{
 			if (node.second != source)

Tests/0003_Graph/0003_TopologicalSortTest.cc

@@ -104,4 +104,41 @@ namespace TopologicalSort
         // Expected output if cycle detection is implemented
         EXPECT_THROW(graph.ShowTopologicalSortResult(), runtime_error);
     }
+
+    TEST(TopoSortTesting, ShowTopoSortResultUsingKahnAlgorithm)
+    {
+        Graph graph;
+
+        graph.PushDirectedEdge(1, 2);
+        graph.PushDirectedEdge(1, 4);
+        graph.PushDirectedEdge(2, 3);
+        graph.PushDirectedEdge(4, 3);
+        graph.PushSingleNode(5);
+        graph.PushDirectedEdge(6, 7);
+        graph.PushDirectedEdge(6, 8);
+        graph.PushDirectedEdge(7, 4);
+        graph.PushDirectedEdge(7, 8);
+        graph.PushDirectedEdge(9, 8);
+
+        graph.KahnTopologicalSort();
+
+        string actualResult = unitTestHelper.SerializeVectorToString(graph.ShowTopologicalSortResult());
+        string expectedResult = "1(1,5) 5(2,7) 6(3,8) 9(4,10) 2(6,11) 7(9,12) 4(13,15) 8(14,17) 3(16,18)";
+
+        EXPECT_EQ(actualResult, expectedResult);
+    }
+
+    // Test with a cyclic graph to verify it can detect cycles
+    TEST(TopoSortTesting, CyclicGraphUsingKahnAlgorithm)
+    {
+        Graph graph;
+        graph.PushDirectedEdge(1, 2);
+        graph.PushDirectedEdge(2, 3);
+        graph.PushDirectedEdge(3, 1);  // Cycle: 1 -> 2 -> 3 -> 1
+
+        graph.KahnTopologicalSort();
+
+        // Expected output if cycle detection is implemented
+        EXPECT_THROW(graph.ShowTopologicalSortResult(), runtime_error);
+    }
 }