Write better code: Day 8 - Graph Coloring

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

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Day 8: Question 1

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

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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.

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markdown guide
 

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
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