kind_of_fair_combination.rb

kind_of_fair_combination.rb

class Array
    def fair_combination
        arr = []
        n = length
        m = (n / 2).floor
 
        # Divide by interval 
        (1..m - 1).each do |j|
            subarr = (0..n - 1).to_a
            sub1 = []
            sub2 = []
            begin
                j.times { sub1.push(subarr.shift) unless subarr.empty? }
                j.times { sub2.push(subarr.shift) unless subarr.empty? }
            end until subarr.empty?
            sub1.concat(sub2).each do |sub|
                arr.push([self[sub], self[(sub + j).modulo(n)]])
            end
        end
 
        # Try to extend for even case 
        if n.even?
            (0..(n / 2) - 1).each do |i|
                arr.push([self[i], self[(i + (n / 2)).modulo(n)]])
            end
        else
            (0..n - 1).each do |i|
                arr.push([self[i], self[(i + m).modulo(n)]])
            end
        end
 
        arr
 
    end
end
 
# p (1..7).to_a.fair_combination
# --> [[1, 2], [3, 4], [5, 6], [7, 1], [2, 3], [4, 5], [6, 7], [1, 3], [2, 4], [5, 7], [6, 1], [3, 5], [4, 6], [7, 2], [1, 4], [2, 5], [3, 6], [4, 7], [5, 1], [6, 2], [7, 3]]