qsort.rb

def qsort(seq)
  return seq if seq.empty?
  p = pivot(seq)
  qsort(left(seq, p)) + [p] + qsort(right(seq, p))
end

def pivot(seq)
  seq.sample
end

def left(seq, p)
  seq.select { |e| e < p }
end

def right(seq, p)
  seq.select { |e| e > p }
end

arr = [ 1, 53, 36, 77, 22, 100, 4, 20 ]
p qsort(arr)