CSCI-1200 Data Structures — Spring 2023
Homework 6 — Inverse Word Search Recursion
In this homework we will build an inverse word search program using the techniques of recursion. The goal
is to construct a grid of letters that one can search to find specific words. Understanding the non-linear word
search program from Lectures 12 & 13 will be helpful in thinking about how you will solve this problem.
We strongly urge you to study and play with that program, including tracing through its behavior using a
debugger or cout statements or both. Please read the entire handout before beginning your implementation.
Your Tasks
For this assignment, you will be given the dimensions (width and height) of a word search puzzle, a set of
words that should appear in the grid (forwards, backwards, up, down, or along any diagonal), and optionally
a set of words that should not appear anywhere in the grid. Each grid cell will be assigned one of the 26
lowercase letters. Note that unlike the non-linear word search problem we discussed in class, we will only
allow words that appear in a straight line (including diagonals). Your task is to output all unique word
search grids that satisfy the requirements. Rotations and mirroring of the board will be considered unique
solutions.
Your program should expect three command line arguments, the name of the input file, the name of the
output file, and a string:
inverse_word_search.exe puzzle2.txt out2.txt one_solution
inverse_word_search.exe puzzle2.txt out2.txt all_solutions
The third argument indicates whether the program should find all solutions, or just one solution. Here’s an
example of the input file format:
The first line specifies the width and height of the grid. Then each line that follows contains a character
and a word. If the character is ’+’, then the word must appear in the grid. If the character is ’-’, then the
word must not appear in the grid. For this first example we show an incorrect solution on the left. Though
it contains the 4 required words, it also contains two of the forbidden words. The solution on the right is a
fully correct solution. This particular problem has 8 solutions including rotations and reflections.
Below is a second example that specifies only positive (required) words. This puzzle has 4 solutions including
rotations and reflections.
When asked to find all solutions, your program should first output the number of solutions and then an
ASCII representation for each solution. See the example output on the course webpage. You should follow
this output closely, however your solutions may be listed in a different order. When asked to find just one
solution, your program should just output the first legal solution it finds (it does not need to count the
number of solutions, nor does it need to be the first solution shown in our output). If the puzzle is impossible
your program should output “No solutions found”.
To implement this assignment, you must use recursion in your search. First you should tackle the problem
of finding and outputting one legal solution to the puzzle (if one exists).
Algorithm Analysis
For larger, more complex examples, this is a really hard problem. Your program should be able to handle
the small puzzles we have created in a reasonable amount of time. You should make up your own test cases
as well to understand this complexity. Include these test cases with your submission (they will be graded).
Summarize the results of your testing, which test cases completed successfully and the approximate “wall
clock time” for completion of each test. The UNIX/WSL time command can be prepended to your command
line to estimate the running time:
time inverse_word_search.exe puzzle1.txt out1.txt one_solution
Once you have finished your implementation and testing, analyze the performance of your algorithm using
order notation. What important variables control the complexity of a particular problem? The width &
height of the grid (w and h), the number of required words (r), the number of forbidden words (f), the
number of letters in each word (l), the number of solutions (s)? In your plain text README.txt file, write
a concise paragraph (< 200 words) justifying your answer. Also include a simple table summarizing the
running time and number of solutions found by your program on each of the provided examples. Note: It’s
ok if your program can’t solve the biggest puzzles in a reasonable amount of time.
IMPORTANT: All students are required to submit their program to the Homework 6 contest (see below).
Extra credit will be awarded for programs that have a strong performance in the contest. You must do this
assignment on your own, as described in the “Collaboration Policy & Academic Integrity” handout. If you
did discuss this assignment, problem solving techniques, or error messages, etc. with anyone, please list their
names in your README.txt file.
FINAL NOTE: If you earn 6 points between Test Cases 3, 4, 5, 6 on Submitty by 11:59pm on Wednesday
March 15th, you may submit your assignment on Friday March 17th without being charged a late day.
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Homework 6 Inverse Word Search Contest Rules
Contest submissions are a separate homework submission. Contest submissions are due March 24th at
11:59pm. You may not use late days for the contest. (The regular homework deadline is Thursday Mar
16th at 11:59pm and late days are allowed for the regular homework submissions.)
You may submit the same code for both the regular homework submission and the contest. Or you
may make a small or significant change for the contest.
Contest submissions do not need to use recursion.
Contest submissions must follow the output specifications and match the formatting of the examples
posted on the course webpage.
We will compile your code with optimizations enabled (g++ -O3 *.cpp). Programs that do not compile,
or do not complete the basic tests in a reasonable amount of time with correct output, will not receive
extra credit.
Programs must be single-threaded and single-process.
We will run your program by redirecting std::cout to a file and measure performance with the UNIX
time command. For example:
time inverse_word_search.exe puzzle1.txt out_puzzle1.txt one_solution
time inverse_word_search.exe puzzle1.txt out_puzzle1_all.txt all_solutions
You may want to use a C++ code profiler to measure the efficiency of your program and identify the
portions of your code that consume most of the running time. A profiler can confirm your suspicions
about what is slow, uncover unexpected problems, and focus your optimization efforts on the most
inefficient portions of the code.
We will be testing with both one solution and all solutions and will highlight the most correct
and the fastest programs.
In the regular non-contest HW6, you may submit up to two interesting new test cases for possible
inclusion in the contest. Name these tests smithj 1.txt and smithj 2.txt (where smithj is your
RCS username). Extra credit will be awarded for interesting test cases that are used in the contest.
Caution: Don’t make the test cases so difficult that your program cannot solve them in a reasonable
amount of time!
In your README contest.txt file, describe the optimizations you implemented for the contest, describe
your new test cases, and summarize the performance of your program on all test cases.
Extra credit will be awarded based on overall performance in the contest