DEV Community

Arjun Rajkumar
Arjun Rajkumar

Posted on • Updated on

Write better code: Day 8 - Graph Coloring

This post originally appeared on Arjun Rajkumar's blog. Arjun is a web developer based in Bangalore, India.

--

Day 8: Question 1

Given an undirected graph with maximum degree DD, find a graph coloring using at most D+1 colors.

-

If you want to follow along, feel free to post your answers in the comment.

My answers are in the comments.
This problem is from InterviewCake.

Discussion (1)

Collapse
arjunrajkumar profile image
Arjun Rajkumar Author

Logic:

  • Each node in the graph has maximum D neighbours.
  • Given than there are maximum D+1 colours, we can assume that for each node there is atleast one color that is not used.
  • So, go thru each node and get the colors of all its neighbours.
  • Check to see which color is not included in this neighbouring color group, and assign the color to it.
def colour_graoh(colors, graph)
  graph.nodes.each do |node|

    all_neighbouring_colors = []

    node.neighbours.each do |neighbour|
      all_neighbouring_colors << neighbour.color if !all_neighbouring_colors.include?(neighbour.color)
    end

    colors.each do |color|
      node.color = color if !all_neighbouring_colors.include?(color)
      break
    end
end