gistfile1.rb

# start off with the hash

timezones = {}

# then build the hash

(-12..12).to_a.each do |i|
  timezones["utc"+i] = 0
end

# now we have a hash with a key for each timezone from "utc-12" to "utc12"

# now we run through the list of tweets

tweets.each do |tweet|
  # we'll assume tweet has some way to access its timezone and that tweet["timezone"] spits out "utc-10", etc
  timezones[tweet["timezone"]] += 1
  # because the value at each key is an integer (starting at 0), each time we encounter the timezone, we simply add one to the value at that key
end

# later when we want to get the number of tweet for a timezone, we do this:

puts timezones["utc-9"]