sorting tournament seeds

Question

I\'m making a HTML/JS powered single/double elimination bracket web app. I am struggling to figure out how to assign the first round matches from a list of seeded teams/players.

Answer 1

I was really intrigued and impressed with Cliff's algorithm here. I think it is very clever. Here is a simple implementation I wrote in ruby. The BYEs are returned as -1.

def seed(n)
  rounded_n = next_power_of_two(n)
  nbr_bits_required=rounded_n.to_s(2).length-1
  binary_seeds = Array.new(rounded_n) {Array.new(nbr_bits_required)}
  binary_seeds[0]=Array.new(nbr_bits_required){0}

  nbr_bits_required.times do |col|    
    1.upto(rounded_n-1) do |row|
      if row % (2**(col+1)) == 0
        #asterisk in the previous row, don't inverse the bit
        binary_seeds[row][col] = binary_seeds[row-1][col]
      else
        #no asterisk in the previous row, inverse the bit
        binary_seeds[row][col] = binary_seeds[row-1][col] == 0 ? 1 : 0
      end
    end
  end

  #output the result in decimal format
  binary_seeds.collect {|bs| s=(bs.join("")).to_i(2)+1; s>n ? -1 : s}
end

def next_power_of_two(n)
  k = 1
  k*=2 while k

Test it out:

seed(8)
=> [1, 8, 5, 4, 3, 6, 7, 2]

seed(6)
=> [1, -1, 5, 4, 3, 6, -1, 2]