Create GraphColoring.py

GraphColoring.py

@@ -0,0 +1,78 @@
+# Python3 program to implement greedy 
+# algorithm for graph coloring 
+
+def addEdge(adj, v, w):
+
+    adj[v].append(w)
+
+    # Note: the graph is undirected
+    adj[w].append(v)  
+    return adj
+
+# Assigns colors (starting from 0) to all
+# vertices and prints the assignment of colors
+def greedyColoring(adj, V):
+
+    result = [-1] * V
+
+    # Assign the first color to first vertex
+    result[0] = 0;
+
+
+    # A temporary array to store the available colors. 
+    # True value of available[cr] would mean that the
+    # color cr is assigned to one of its adjacent vertices
+    available = [False] * V
+
+    # Assign colors to remaining V-1 vertices
+    for u in range(1, V):
+
+        # Process all adjacent vertices and
+        # flag their colors as unavailable
+        for i in adj[u]:
+            if (result[i] != -1):
+                available[result[i]] = True
+
+        # Find the first available color
+        cr = 0
+        while cr < V:
+            if (available[cr] == False):
+                break
+
+            cr += 1
+
+        # Assign the found color
+        result[u] = cr 
+
+        # Reset the values back to false 
+        # for the next iteration
+        for i in adj[u]:
+            if (result[i] != -1):
+                available[result[i]] = False
+
+    # Print the result
+    for u in range(V):
+        print("Vertex", u, " --->  Color", result[u])
+
+# Driver Code
+if __name__ == '__main__':
+
+    g1 = [[] for i in range(5)]
+    g1 = addEdge(g1, 0, 1)
+    g1 = addEdge(g1, 0, 2)
+    g1 = addEdge(g1, 1, 2)
+    g1 = addEdge(g1, 1, 3)
+    g1 = addEdge(g1, 2, 3)
+    g1 = addEdge(g1, 3, 4)
+    print("Coloring of graph 1 ")
+    greedyColoring(g1, 5)
+
+    g2 = [[] for i in range(5)]
+    g2 = addEdge(g2, 0, 1)
+    g2 = addEdge(g2, 0, 2)
+    g2 = addEdge(g2, 1, 2)
+    g2 = addEdge(g2, 1, 4)
+    g2 = addEdge(g2, 2, 4)
+    g2 = addEdge(g2, 4, 3)
+    print("\nColoring of graph 2")
+    greedyColoring(g2, 5)