计算用于在python中为图形着色的颜色数量

Question

I need help with my code to count the number of colors that used to color the graph I wrote a small code to print a list of colors and now I need to count them

import networkx as nx
g = nx.Graph()
g.add_nodes_from([1,2,3,4,5])
g.add_edges_from([(1,2),(1,3),(1,4),(1,5),(4,5)])
C = set(xrange(12))
color = {}

for u in g:
    interdits = set([color[v] for v in g.neighbors(u) if color.has_key(v)])
    color[u] = min(C-interdits)

print color

the output :

 {1: 0, 2: 1, 3: 1, 4: 1, 5: 2} 

instead of this output I want to count the colors so the result should be 3 Any idea or help?? Thanks in advance

Answer 1

You should definitely read through a Python tutorial . You might also want to use ipython or IDLE or something where you can easily see what methods are living inside an object without having to consult the docs, which is an easy way to experiment. dir(some_object_name) works too but I don't find it as convenient as hitting tab in ipython, but YMMV.

In any case, once you have your color variable:

>>> color
{1: 0, 2: 1, 3: 1, 4: 1, 5: 2}
>>> color.values()
[0, 1, 1, 1, 2]
>>> set(color.values())
set([0, 1, 2])
>>> len(set(color.values()))
3

(And just to make sure, this the number of colours you used , not the minimum number of colours needed.)

Answer 2

The highest number color used can be found with

max(color.values())

but they're numbered from zero so you probably want

max(color.values()) + 1

While it likely doesn't really matter, this doesn't require building a list of all the colors used, or hashing each entry, unlike the set method.

Also, has_key is deprecated. Use v in color instead.