GREEDY ALGORITHM:

import networkx as nx

import matplotlib.pyplot as plt

import time

def color_nodes(G):

    color_map = {}

    colormap = [] 

    for node in sorted(G, key=lambda x: len(G[x]), reverse=True):

        neighbor_colors = set(color_map.get(neigh) for neigh in G[node]) 

    #Nodes sorted first, descending based on degree     for node in sorted(G, key=lambda x: 

len(G[x]), reverse=True):         neighbor_colors = set(color_map.get(neigh) for neigh in 

G[node]) 

        color_map[node] = next(color for color in range(len(G))if color not in neighbor_colors)

    i=0

    #print(color_map)

    while i<color_map.__len__():

        if color_map[i]==0: 

            colormap.append('yellow')

        elif color_map[i]==1: 

            colormap.append('purple')

        elif color_map[i]==2: 

            colormap.append('lightseagreen')

        elif color_map[i]==3: 

            colormap.append('blue')

        elif color_map[i]==4: 

            colormap.append('magenta')

        elif color_map[i]==5: 

            colormap.append('cyan')

        elif color_map[i]==6: 

            colormap.append('red')

        elif color_map[i]==7: 

            colormap.append('blue_violet')

        elif color_map[i]==8: 

            colormap.append('orange')

        elif color_map[i]==9: 

            colormap.append('lightsalmon')

        elif color_map[i]==10: 

            colormap.append('darkcyan')

        elif color_map[i]==11: 

            colormap.append('green')

        elif color_map[i]==12: 

            colormap.append('lightpink')

        elif color_map[i]==13:

            colormap.append('y')

        i=i+1

    plt.subplot(212) 

    plt.title("Result of Greedy Algorithm") 

    nx.draw(G, with_labels=True, font_weight='bold',node_color=colormap)

#    if _name_ == '_main_':

t = time.process_time()

# Graph drawing

G = nx.Graph()

G.add_nodes_from([0,1,2,3,4,5,6,7,8,9,10,11,12])#13 nodes

G.add_edges_from([(0,1),(0,2),(1,4),(2,4),(2,3),(3,5),(4,5),(5,7),(5,6),(7,9),(6,8),(8,9),(9,11),(

8,10),(10,12),(11,12)])

plt.subplot(211)

plt.title("Initial Graph")

nx.draw_shell(G, with_labels=True, font_weight='bold', node_color='lightgray')

color_nodes(G)

print("Time elapsed:",time.process_time() - t)

plt.show()