Assignment 4. Backtracking

Due Friday, October 16 at 11:59 pm Pacific

  • Submissions received by due date receive a small on-time bonus.
  • All students are granted a pre-approved extension or "grace period" of 48 hours after the due date. Late submissions are accepted during the grace period with no penalty.
  • The grace period expires Sun, Oct 18 at 11:59 pm Pacific, after which we cannot accept further late submissions.
  • In this course, we express all date/times in Pacific time GMT -7. Our Paperless submission system also displays/records due dates and submission times in Pacific time.

Last week's assignment introduced you to the intriguing world of recursion and built your solid base of recursive fundamentals. This week we pivot towards applying the powerful nature of recursive backtracking to solve real-world problems. As is typical in recursive problem-solving, you'll likely spend the bulk of your time wrapping your head around the "thinking recursively" part, but once writing the actual code, you'll find that a rather concise algorithm is all that's needed to solve the task. That sparse elegance can sometimes seem incongruous with how hard you had to work for it. Start early to give yourself enough time to let these deep and powerful ideas percolate to full understanding. When you put the finishing touches on these problems, you will have earned your rightful place as a master in the way of recursive problem-solving.

This assignment is to be completed individually. Working in pairs/groups is not permitted.

Learning goals

After completing this assignment, you will be able to…

  • Appreciate the elegance and power of recursive problem-solving and identify problems that are well-suited to be solved recursively
  • Apply the choose/explore/unchoose pattern of recursive backtracking to explore all possibilities throughout a search space
  • Implement more advanced recursive algorithms to solve problems that cannot be easily solved using an iterative approach

Assignment parts

This assignment consists of a warmup exercise and three separate problems to solve using recursive backtracking.

  • Warmup

    Practice with testing and debugging recursive functions.

  • Text Predict

    Predict a user's intended word when typed on old-style phone keypad.

  • Scoring Boggle

    Find all words on a given Boggle board and tally the maximum possible score.

  • Voting Power

    Compute the voting power of the different blocks in a block-voting system such as the U.S. Electoral College.

  • Feedback Survey

    Complete a mid-quarter evaluation to let us know your thoughts on how the course has been going so far and how we can best improve the learning experience going forward!

Getting started

We provide a ZIP of the starter project. Download the zip, extract the files, and double-click the .pro file to open the project in Qt Creator.

📦 Starter code

The source files you will edit are predict.cpp, boggle.cpp, and voting.cpp. Additionally, you will answer questions in short_answer.txt.


Here are some resources that you might find helpful for this assignment:

Getting help

We have several channels where you can reach out to the course staff: post on Ed, email your section leader, join in at office hours, or sign up for one-one-one help at the LaIR. For questions specific to your code, coming to Lair is your best bet. If you cannot attend LaIR due to timezone issues, you may post your question on Ed. However, you must use a private post if you are including code so that you are not posting your solutions for the whole class to see.


Before you call it done, run through our submit checklist to be sure all your t's are crossed and i's dotted. Then upload your completed files to Paperless for grading.

Please submit only the files you edited; for this assignment, these files will be:

  • predict.cpp
  • boggle.cpp
  • voting.cpp
  • short_answer.txt

🏁 Submit to Paperless

Note: On Paperless, all due dates and submission times are expressed in Pacific time.