AtCoder ABC #058

abc058-a.rb

a, b, c = gets.chomp.split(" ").map(&:to_i)
if b - a == c - b then
  puts "YES"
else
  puts "NO"
end

abc058-b.rb

o = gets.chomp.split("")
e = gets.chomp.split("")

o.zip(e).each do |a, b|
  print(a, b)
end
puts

abc058-c.rb

n = gets.chomp.to_i
ret = Hash.new{|h, k| h[k] = Array.new()}
n.times do
  s = gets.chomp.split("")
  h = Hash.new(0)
  s.each do |c|
    h[c] += 1
  end
  h.each do |k, v|
    ret[k] << h[k]
  end
end
ret.keys.sort.each do |k|
  if ret[k].size == n then
    l = ret[k].min
    print(k * l)
  end
end
puts