k difference for interview street challenge

gistfile1.txt

nk = STDIN.gets.split(" ")
nums_str = STDIN.gets.split(" ")

n = nk[0].to_i
k = nk[1].to_i

nums = nums_str.collect{|num| num.to_i}.sort!

h = {}
count = 0
nums.each do |n|
  if h[(n-k).to_s]
    count += 1
  end
  h[n.to_s] = n
end

puts count