Knight's Travail: Recursive Solution

Question

The problem is to create a data structure, similar to a binary search tree that can list all possible moves a knight (in chess) can make on a 8x8 board. I came up with a single node class with the current location, a parent and 8 possible children which represent the 8 possible moves a knight can make.

class KnightNode
  attr_accessor :location, :child_1, :child_2, :child_4, :child_5, :child_7, :child_8, :child_10, :child_11
  def initialize(location = nil)
    @location = location
    @parent = nil
    #8 possible children, label them as if they were hands on a clock
    @child_1 = nil
    @child_2 = nil
    @child_4 = nil
    @child_5 = nil
    @child_7 = nil
    @child_8 = nil
    @child_10 = nil
    @child_11 = nil
  end
end

def generate_tree(location)
  root = KnightNode.new(location)
  move1 = [root.location[0] + 1,root.location[1] + 2]
  move2 = [root.location[0] + 2,root.location[1] + 1]
  move4 = [root.location[0] + 2,root.location[1] - 1]
  move5 = [root.location[0] + 1,root.location[1] - 2]
  move7 = [root.location[0] - 1,root.location[1] - 2]
  move8 = [root.location[0] - 2,root.location[1] - 1]
  move10 = [root.location[0] - 2,root.location[1] - 1]
  move11 = [root.location[0] - 1,root.location[1] + 2]
  move1[0] > 7 && move1[1] > 7 ? root.child_1 = nil : root.child_1 = generate_tree(move1)
  move2[0] > 7 && move2[1] > 7 ? root.child_2 = nil : root.child_2 = generate_tree(move2)
  move4[0] > 7 && move4[1] < 0 ? root.child_4 = nil : root.child_4 = generate_tree(move4)
  move5[0] > 7 && move5[1] < 7 ? root.child_5 = nil : root.child_5 = generate_tree(move5)
  move7[0] < 0 && move7[1] < 7 ? root.child_7 = nil : root.child_7 = generate_tree(move7)
  move8[0] < 0 && move8[1] < 0 ? root.child_8 = nil : root.child_8 = generate_tree(move8)
  move10[0] < 0 && move10[1] < 0 ? root.child_10 = nil : root.child_10 = generate_tree(move10)
  move11[0] < 0 && move11[1] > 7 ? root.child_11 = nil : root.child_11 = generate_tree(move11)
  return root
end

generate_tree([3,3])

When I run this code, I run into a SystemStackError. My guess is that my recursion is going through an infinite loop, however I do not see the problem. Thanks in advance!

score 0 · Answer 1 · answered Jun 21 '18 at 04:33

I don't see any way you actually terminate the search. You prune if it goes off the board, but you need to either artificially limit it to 64 (number of squares on the board) and/or track where it has already visited and not let it visit that square again.

Knight's Travail: Recursive Solution

1 Answers1