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+# Exercise 2.2 - Solution
+
+There is no official solution for this exercise--you need rely on your
+current Python knowledge.  However, there are a few tips that can
+help.
+
+- For problems where you need to determine uniqueness, use a set. Sets aren't allowed to
+have duplicates.
+
+- If you need to tabulate data, consider using a dictionary that maps keys to a numeric
+count.  For example, to count rides on each bus route, you could make a dictionary that
+maps the route name to the total ride count for that route.  A `Counter` object from
+`collections` is perfect for this task.
+
+- If you need to keep data in order or sort data, store it in a list.
+
+- You can make Python data structures out of almost anything.  For
+example, dictionaries of sets, nested dictionaries, etc.  You might
+need to do this to answer questions 3 and 4.
+
+
+
+[Back](ex2_2.md)