CMPS 12B-02辅导、讲解javaHow to Place Your Queens

CMPS 12B-02, Fall 2017

HW1: How to Place Your Queens

Due: Oct 15, 2017 by 11:59pm

All assignments must be submitted through git. Please look at the Piazza guide

on submitting assignments.

Please follow the naming conventions properly. Please look at the Piazza guide

on the checking script. Run the checking script to make sure your files are named

correctly. You will get no credit if the checking script fails!

Follow instructions, and carefully read through the input/output formats.

Clearly acknowledge sources, and mention if you discussed the problems with

other students or groups. In all cases, the course policy on collaboration applies, and

you should refrain from getting direct answers from anybody or any source. If in

doubt, please ask the Instructor or TAs.

1 Problem description

Main objective: Solve the n queens problems. You have to place n queens on an n ×

n chessboard such that no two attack each other. Important: the chessboard should be

indexed starting from 1, in standard (x, y) coordinates. Thus, (4, 3) refers to the

square in the 4th column and 3rd row.

We have a slight twist in this assignment. We will take as input the position of

one queen, and have to generate a solution with a queen in this position.

Specifics: You should provide a Makefile. On running make, it should create

“NQueens.jar”. You should run the jar with two command line arguments: the first is

an input file, the second is the output file. For example, we would call the command:

java -jar NQueens.jar in.txt solution.txt

The file in.txt will have inputs to the main program (as described below), and

the file solution.txt will have the desired solution.

Each line of the input file corresponds to a different instance. Each line of the

input file will have three integers: the chessboard size, the column where the input

queen is placed, and the row where the input queen is placed. For example, the file

may look like:

7 3 2

4 1 1

The first line means we have a 7 × 7 chessboard, with one queen placed at (3, 2).

We wish to place 6 more queens so that none of the 7 queens attack any other. The

second line means we have a 4 × 4 chessboard, with one queen at (1, 1). We wish to

place 3 more queens without any attacks. So on and so forth.

Output: On running the command, the following should be printed in the output

file. For each line of the input file, there is a line in the output file with the placement

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of queens.

If there is no solution to the problem, print “No solution” (with a newline at the

end)

If there is a solution, print the position of each queen as <column> <space>

<row> <space> followed by the position for the next queen. The positions

should be in increasing order of column, so first column first, second column

second, etc. Please follow this format exactly, so that the checking script works

for you. The last character on the line will be a space, then followed by a

newline. This format should make your code easier to write.

For example, the output for the input described above could be:

1 1 2 5 3 2 4 6 5 3 6 7 7 4

No solution

Observe how “3 2” is part of the first solution, since we started with a queen

there. The solution is not unique, so your code might find some other placement. On

the other hand, a 4 × 4 chessboard with a queen at (1, 1) has no solution.

Helper code: Under HW1 on Piazza, you will find a java file that prints out your

solution on a chessboard (with queen positions) on to your console. This is extremely

helpful in checking if your solution is correct. Compile and execute the java code on

your terminal using the commands below:

javac PrintSolutionHelper.java

java PrintSolutionHelper <your output file>

For each line in your output file that has a list of queens positions, the console will

print the chessboard with queens on then. (The code is actually pretty interesting!)

Example commands and outputs: On Piazza, under HW1, you will find a file

named HW1examples.zip. Download and unzip it. There are four files:

test-input.txt, test-output.txt. If you run your program with

input file test-inputs.txt, the output file should be exactly the same as

test-outputs.txt. This will be used by the checking script, and will

need to be in your solution folder.

more-input.txt, more-output.txt. The former file has, ahem,

more inputs, and the latter file has the outputs. For these instances, the

corresponding outputs might not be unique. So, your solution may be different

from what is given, since there can be numerous solutions

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What to submit: Push all your java source files. There is no restriction on

format or how you name them. We only require that you have a makefile called

“Makefile”. On running make, it should provide a jar file called “NQueens.jar”. The

checking code uses the test files test-input.txt, test-output.txt.

2 Grading

Your code should terminate within 3 minutes for all runs (maximum chessboard size

will be 14). You get no credit for a run that does not provide a proper output.

1. (10 points) For a full solution as described above.

2. (9 points) Only solves the problem when the input queen is in the first column.

(This makes your recursive code a lot simpler to write.) When the input queen

is not in the first column, just print “No solution”.

3. (8 points) Only solves for chessboards at most 6 × 6. You can set up 12 nested

loops (6 for rows and 6 for columns) that simply try all possible placements of

6 queens.

4. (7 points) Only solves for chessboards at most 4 × 4.

3 General Rules

All HWs and Labs must be done individually. All program source files you turn in

for this and other assignments should begin with a comment block giving your name

and cruzid, a short description of its role in the project, the file name, and any special

instructions for compiling and/or running it. Be sure to create a README file that

lists all the files being submitted (including README), along with any special notes

to the grader.

Please run the checking script as given on Piazza (under Resources?General

Resources) to verify your file names. Piazza has a guide with instructions of running

it. If your solution/submission does not pass the checking script, you will get no

credit.

You should use "git commit –a –m 'msg' " and "git push" frequently (at least once per

session). It is a great way to avoid losing your work. To actually "submit" your

assignment, while in the assignment directory (e.g. HW1 for this assignment) and

after having done "git push" of your latest work, type "git log".