Educational Codeforces Round 3

cfEdu3-a-USBFlashDrives.rb

n = gets.chomp.to_i
m = gets.chomp.to_i
a = []
n.times do
  a << gets.chomp.to_i
end
res = 0
a.sort.reverse.each do |i|
  break if m <= 0
  m -= i
  res += 1
end
puts res

cfEdu3-b-TheBestGift.rb

n, m = gets.chomp.split(" ").map(&:to_i)
books = gets.chomp.split(" ").map(&:to_i)
dic = Hash.new(0)
res = 0
books.each do |k|
  dic[k] += 1
end
(1..m).to_a.combination(2) do |i, j|
    res +=  dic[i] * dic[j]
end
puts res

cfEdu3-c-LoadBalancing.rb

# [Editorial of Educational Codeforces Round 3 - Codeforces](http://codeforces.com/blog/entry/22187)
n = gets.chomp.to_i
m = gets.chomp.split(" ").map(&:to_i).sort
msum = m.inject(:+)
mmod = msum % n
if mmod == 0
  mm = Array.new(n, msum / n)
else
  mm = Array.new(n - mmod, msum / n) + Array.new(mmod, msum / n + 1)
end
res = 0
m.zip(mm).each do |a, b|
  res += (a - b).abs
end
puts res / 2