A greedy algorithm for graph coloring

Author: sudesh1611

Greedy/Greedy_Graph_Coloring/GreedyGraphColoring.cpp

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+/* **** A Greedy algorithm that never uses more than D+1 colors to color all the vertices of a graph, where D is the maximum degree in the graph  *** */
+/* **** Complexity = O(V^2 + E) where V is number of vertices and E is number of edges *** */
+/* **** This is written in C++14 *** */
+
+#include <iostream>
+#include <vector>
+#include <map>
+#include <set>
+using namespace std;
+
+struct Edge {
+    int sourceVertex, destinationVertex;
+};
+
+//You can add Other Colors too
+string color[] =
+{
+    "", "BLUE", "GREEN", "RED", "YELLOW", "ORANGE", "PINK",
+    "BLACK", "BROWN", "WHITE", "PURPLE", "VOILET"
+};
+
+class Graph
+{
+    public:
+    vector<int> *adjacencyList;
+    Graph(vector<Edge> const &edges, int N)
+    {
+        adjacencyList = new vector<int>[N];
+        for (int i = 0; i < edges.size(); i++)
+        {
+            int src = edges[i].sourceVertex;
+            int dest = edges[i].destinationVertex;
+            adjacencyList[src].push_back(dest);
+            adjacencyList[dest].push_back(src);
+        }
+    }
+    ~Graph() {
+        delete[] adjacencyList;
+    }
+};
+
+void colorGraph(const Graph &graph, int N)
+{
+    map<int, int> result;
+    for (int u = 0; u < N; u++)
+    {
+        set<int> assigned;
+        for (int i : graph.adjacencyList[u]) {
+            if (result[i]) {
+                assigned.insert(result[i]);
+            }
+        }
+        int color = 1;
+        for (auto &c: assigned ) {
+            if (color != c) {
+                break;
+            }
+            color++;
+        }
+        result[u] = color;
+    }
+    for (int v = 0; v < N; v++) {
+        cout << "Color assigned to vertex " << v << " is "
+             << color[result[v]] << '\n';
+    }
+}
+
+int main()
+{
+    int N;
+    cout<<"\nEnter number of vertices in the graph : ";
+    cin>>N;
+
+    int E;
+    cout<<"\nEnter number of edges in the graph : ";
+    cin>>E;
+
+    int temp1, temp2;
+	cout << "\nEnter edges in pair ,where each pair is represented by starting vertex and ending vertex.";
+	cout<<"\nVertex number starts from 0 till "<<N-1;
+	cout << "\nFor Example, edge between vertex 4 and vertex 5 is given like \n4 5\n";
+
+	vector<Edge> edges;
+	int counter=E;
+	while(E--)
+    {
+        temp1=-1;
+        temp2=-1;
+
+        while(temp1<0 || temp2<0 || temp1>=N || temp2>=N)
+        {
+            cout << "\nEnter Edge "<< counter - E -1<<" According to above format\n";
+            cin>>temp1;
+            cin>>temp2;
+        }
+        edges.push_back({temp1,temp2});
+
+    }
+    /*
+    edges =
+    {
+        {0, 1}, {0, 4}, {0, 5}, {4, 5}, {1, 4}, {1, 3}, {2, 3}, {2, 4}
+    };
+    */
+    Graph graph(edges, N);
+    colorGraph(graph, N);
+    return 0;
+}