Important Notice:

Practice-It will be discontinued as of November 1st, 2024. After this date, the website will remain online for a transitional period, but login will be restricted to University of Washington NetID authentication. This marks the next phase towards the platform's full retirement. Thank you for your use and support of the application over the years.

If you are looking for an alternative, a similar tool, CodeStepByStep, was developed independently by the original author of Practice-It, and is available at codestepbystep.com**

logo Practice-It logo

Main Page → Problems → Solve a Problem

BJP5 Exercise 11.7: countCommon

Language/Type: Java Collections Lists Sets and Maps
Author: Whitaker Brand (on 2019/09/19)

Write a method countCommon that takes two Lists of integers as parameters and returns the number of unique integers that occur in both lists. Use one or more Sets as storage to help you solve this problem.

For example, if one list contains the values [3, 7, 3, -1, 2, 3, 7, 2, 15, 15] and the other list contains the values [-5, 15, 2, -1, 7, 15, 36], your method should return 4 (because the elements -1, 2, 7, and 15 occur in both lists).

Type your solution here:


This is a method problem. Write a Java method as described. Do not write a complete program or class; just the method(s) above.

You must log in before you can solve this problem.


Log In

If you do not understand how to solve a problem or why your solution doesn't work, please contact your TA or instructor.
If something seems wrong with the site (errors, slow performance, incorrect problems/tests, etc.), please

Is there a problem? Contact a site administrator.