array_in_hash.rb

# I struggled how to add input data to an array in a hash value and these art some
# ways to do. [See more examples](http://judge.u-aizu.ac.jp/onlinejudge/solution.jsp?pid=0105#6).

#Using an array hash[word] = [page.to_i]
# and using has_key?
hash = {}
while n = gets
  word, page = n.split
  hash.has_key?(word) ?  hash[word] << page.to_i :  hash[word] = [page.to_i]
end

# Using ||=
# [Read this](http://www.rubyinside.com/what-rubys-double-pipe-or-equals-really-does-5488.html)

$<.each_line do |line|
  word, page = line.split
  hash[word] ||= []
  hash[word] << page.to_i
end

# Using hash.key?
dic = {}
while line = gets
  k, v = line.chomp.split
  if dic.key?(k)
    dic[k] << v.to_i
  else
    dic.store(k, [v.to_i])
  end
end