Sync from fork

include/CXXGraph/Graph/Algorithm/welshPowellColoring_impl.hpp

@@ -2,7 +2,57 @@
 // Created by jjsm on 1/22/24.
 //
 
-#ifndef CXXGRAPH_WELSHPOWELLCOLORING_H
-#define CXXGRAPH_WELSHPOWELLCOLORING_H
+#ifndef CXXGRAPH_WELSHPOWELLCOLORING_IMPL_H__
+#define CXXGRAPH_WELSHPOWELLCOLORING_IMPL_H__
 
-#endif  // CXXGRAPH_WELSHPOWELLCOLORING_H
+#pragma once
+
+#include "CXXGraph/Graph/Graph_decl.h"
+
+namespace CXXGraph {
+template <typename T>
+std::map<Node<T>, int> Graph<T>::welshPowellColoring() const {
+  auto adjMatrix = *getAdjMatrix();
+  std::unordered_map<std::shared_ptr<const Node<T>>, int> degreeOfVertexMap = {};
+
+  // Find the degree of each vertex and put them in a map
+  for (auto &[nodeFrom, nodeToEdgeVec] : adjMatrix) {
+    degreeOfVertexMap[nodeFrom] = nodeToEdgeVec.size();
+  }
+
+  // Transform the map to the vector to sort
+  std::vector<std::pair<std::shared_ptr<const Node<T>>, int>> degreeOfVertexVector(degreeOfVertexMap.begin(), degreeOfVertexMap.end());
+
+  // Sort them based on the vertex degree
+  std::sort(degreeOfVertexVector.begin(), degreeOfVertexVector.end(), [](const auto& left, const auto& right) {
+    return left.second > right.second;
+  });
+
+  // Create a new map of coloring, where the keys are the nodes, and the value is the color order (assigned by integer)
+  std::map<Node<T>, int> mapOfColoring;
+  for (auto &[nodeFrom, _] : adjMatrix) {
+    mapOfColoring[*nodeFrom] = 0;
+  }
+
+  // Going down the list of vertex based on degrees
+  for (const auto& [node, _] : degreeOfVertexVector) {
+    // Find the smallest unused color for the current vertex
+    std::vector<int> usedColors(degreeOfVertexVector.size() + 1, 0);
+
+    for (const auto &[neighbor, _] : adjMatrix[node]) {
+      usedColors[mapOfColoring[*neighbor]] = 1;
+    }
+
+    // Assign the smallest unused color to the current vertex
+    for (int c = 1; c < usedColors.size(); c++) {
+      if (usedColors[c] == 0) {
+        mapOfColoring[*node] = c;
+        break;
+      }
+    }
+  }
+
+  return mapOfColoring;
+}
+}
+#endif  // CXXGRAPH_WELSHPOWELLCOLORING_IMPL_H__

include/CXXGraph/Graph/Graph.h

@@ -41,6 +41,7 @@
 #include "CXXGraph/Graph/Algorithm/Tarjan_impl.hpp"
 #include "CXXGraph/Graph/Algorithm/TopologicalSort_impl.hpp"
 #include "CXXGraph/Graph/Algorithm/TransitiveReduction_impl.hpp"
+#include "CXXGraph/Graph/Algorithm/welshPowellColoring_impl.hpp"
 
 // IO Operation
 #include "CXXGraph/Graph/IO/IOUtility_impl.hpp"

include/CXXGraph/Graph/Graph_decl.h

@@ -795,6 +795,17 @@ class Graph {
   virtual double fordFulkersonMaxFlow(const Node<T> &source,
                                       const Node<T> &target) const;
 
+  /**
+    * @brief Welsh-Powell Coloring algorithm
+    * @return a std::map of keys being the nodes and the values being the color
+    * order (by integer) starting from 1.
+    * Source :
+    *          https://www.youtube.com/watch?v=SLkyDuG1Puw&ab_channel=TheLogicalLearning
+    *          https://www.geeksforgeeks.org/welsh-powell-graph-colouring-algorithm/
+    *          https://www.tutorialspoint.com/de-powell-graph-colouring-algorithm
+   */
+  virtual std::map<Node<T>, int> welshPowellColoring()  const;
+
   /**
    * \brief
    * This function writes the graph to an output file