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日期:2021-04-17 11:27

Assignment 2

COMP9021, Term 1, 2021

1. General matter

1.1. Aims. The purpose of the assignment is to:

? design and implement an interface based on the desired behaviour of an application program;

? practice the use of Python syntax;

? develop problem solving skills.

1.2. Submission. Your program will be stored in a file named tangram.py. After you have developed and

tested your program, upload it using Ed (unless you worked directly in Ed). Assignments can be submitted

more than once; the last version is marked. Your assignment is due by April 26, 10:00pm.

1.3. Assessment. The assignment is worth 13 marks. It is going to be tested against a number of input files.

For each test, the automarking script will let your program run for 30 seconds.

Late assignments will be penalised: the mark for a late submission will be the minimum of the awarded mark

and 13 minus the number of full and partial days that have elapsed from the due date.

The outputs of your programs should be exactly as indicated.

1.4. Reminder on plagiarism policy. You are permitted, indeed encouraged, to discuss ways to solve the

assignment with other people. Such discussions must be in terms of algorithms, not code. But you must

implement the solution on your own. Submissions are routinely scanned for similarities that occur when students

copy and modify other people’s work, or work very closely together on a single implementation. Severe penalties

apply.

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2. Background

The game of tangram consists in creating shapes out of pieces. We assume that each piece has its own colour,

different to the colour of any other piece in the set we are working with. Just for reference, here is the list of

colours that are available to us (you will not make use of this list):

https://www.w3.org/TR/2011/REC-SVG11-20110816/types.html#ColorKeywords

A representation of the pieces will be stored in an .xml file thanks to a simple, fixed syntax.

2.1. Pieces. Here is an example of the contents of the file pieces_A.xml, typical of the contents of any file of

this kind (so only the number of pieces, the colour names, and the various coordinates can differ from one such

file to another—we do not bother with allowing for variations, in the use of space in particular).

<svg version="1.1" xmlns="http://www.w3.org/2000/svg">

<path d="M 50 50 L 50 90 L 90 90 z" fill="red"/>

<path d="M 160 170 L 160 130 L 120 130 z" fill="green"/>

<path d="M 200 30 L 180 30 L 180 50 L 220 50 z" fill="blue"/>

<path d="M 40 100 L 40 140 L 60 140 L 60 120 z" fill="yellow"/>

<path d="M 210 70 L 230 90 L 270 90 L 270 50 L 230 50 z" fill="purple"/>

<path d="M 180 130 L 180 170 L 220 210 L 240 190 z" fill="olive"/>

<path d="M 100 200 L 120 180 L 80 140 L 80 180 z" fill="magenta"/>

</svg>

Opened in a browser, pieces_A.xml displays as follows:

Note that the coordinates are nonnegative integers. This means that the sets of pieces we consider rule out

those of the traditional game of tangram, where √

2 is involved everywhere...

We require every piece to be a convex polygon. An .xml file should represent a piece with n sides (n ≥ 3) by

an enumeration of n pairs of coordinates, those of consecutive vertices, the first vertex being arbitrary, and the

enumeration being either clockwise or anticlockwise.

The pieces can have a different orientation and be flipped over. For instance, the file pieces_AA.xml whose

contents is

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<svg version="1.1" xmlns="http://www.w3.org/2000/svg">

<path d="M 90 90 L 90 110 L 110 110 L 110 70 z" fill="yellow"/>

<path d="M 130 80 L 170 120 L 170 80 z" fill="red"/>

<path d="M 290 150 L 270 170 L 210 110 L 250 110 z" fill="olive"/>

<path d="M 190 120 L 190 160 L 210 180 L 230 160 z" fill="magenta"/>

<path d="M 320 80 L 300 100 L 280 100 L 280 80 z" fill="blue"/>

<path d="M 320 150 L 360 150 L 320 190 z" fill="green"/>

<path d="M 230 30 L 230 70 L 210 90 L 190 70 L 190 30 z" fill="purple"/>

</svg>

and which displays as

represents the same set of pieces (the fact that the latter appear as smaller than the former is just due to the

different scaling of the included pdf’s; the sizes of the pieces are actually the same in terms of the coordinates

of their vertices).

The pieces can overlap, but that does not concern us. In practice, we will just use representations where the

pieces do not overlap as that allows us to visualise the pieces properly when we open the corresponding .xml

file, but it is just for convenience and irrelevant to the tasks we tackle.

2.2. Shapes. A representation of a shape is provided thanks to an .xml file with the same structure, storing

the coordinates of the vertices of just one polygon.

The file shape_A_1.xml whose contents is

<svg version="1.1" xmlns="http://www.w3.org/2000/svg">

<path d="M 30 20 L 110 20 L 110 120 L 30 120 z" fill="grey"/>

</svg>

and which displays as

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is such an example. The file shape_A_2.xml whose contents is

<svg version="1.1" xmlns="http://www.w3.org/2000/svg">

<path d="M 50 10 L 90 10 L 90 50 L 130 50 L 130 90 L 90 90 L 90 130...

...L 50 130 L 50 90 L 10 90 L 10 50 L 50 50 z" fill="brown"/>

</svg>

and which displays as

is another such example.

Contrary to pieces, shapes are not assumed to be convex polygons. Still they are assumed to be simple polygons

(the boundary of a simple polygon does not cross itself; in particular, it cannot consist of at least 2 polygons

that are connected by letting two of them just “touch” each other at one of their vertices—e.g., two rectangles

such that the upper right corner of one rectangle is the lower left corner of the other rectangle; that is not

allowed).

Whereas you will have to check that the representation of the pieces in an .xml file satisfies our constraints,

you will not have to do so for the representation of a shape; you can assume that any shape we will be dealing

with satisfies our constraints.

2.3. Tangrams. The first shape can be built from our set of pieces, in many ways. Here is one, given by the

file tangram_A_1_a.xml whose contents is

<svg version="1.1" xmlns="http://www.w3.org/2000/svg">

<path d="M 30 60 L 30 20 L 70 20 z" fill="green"/>

<path d="M 50 120 L 50 80 L 70 60 L 90 80 L 90 120 z" fill="purple"/>

<path d="M 30 100 L 90 40 L 70 20 L 30 60 z" fill="olive"/>

<path d="M 70 60 L 110 100 L 110 60 L 90 40 z" fill="magenta"/>

<path d="M 50 120 L 30 120 L 30 100 L 50 80 z" fill="blue"/>

<path d="M 110 20 L 70 20 L 110 60 z" fill="red"/>

<path d="M 110 100 L 110 120 L 90 120 L 90 80 z" fill="yellow"/>

</svg>

and which displays as follows.

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Here is another one, given by the file tangram_A_1_b.xml whose contents is

<svg version="1.1" xmlns="http://www.w3.org/2000/svg">

<path d="M 30 20 L 50 20 L 50 60 L 30 40 z" fill="yellow"/>

<path d="M 50 60 L 50 20 L 90 20 L 90 60 L 70 80 z" fill="purple"/>

<path d="M 70 120 L 110 80 L 110 120 z" fill="green"/>

<path d="M 90 20 L 110 20 L 110 40 L 90 60 z" fill="blue"/>

<path d="M 30 120 L 30 80 L 70 120 z" fill="red"/>

<path d="M 70 120 L 30 80 L 30 40 L 90 100 z" fill="olive"/>

<path d="M 70 80 L 110 40 L 110 80 L 90 100 z" fill="magenta"/>

</svg>

and which displays as follows.

The second shape can also be built from our set of pieces, in many ways. Here is one, given by the file

tangram_A_2_a.xml whose contents is

<svg version="1.1" xmlns="http://www.w3.org/2000/svg">

<path d="M 50 10 L 70 10 L 70 30 L 50 50 z" fill="yellow"/>

<path d="M 70 10 L 90 10 L 90 50 L 70 30 z" fill="blue"/>

<path d="M 10 50 L 50 50 L 10 90 z" fill="green"/>

<path d="M 90 50 L 130 50 L 130 90 z" fill="red"/>

<path d="M 10 90 L 70 30 L 90 50 L 50 90 z" fill="olive"/>

<path d="M 90 50 L 130 90 L 90 90 L 70 70 z" fill="magenta"/>

<path d="M 70 70 L 90 90 L 90 130 L 50 130 L 50 90 z" fill="purple"/>

</svg>

and which displays as follows.

6

Here is another one, given by the file tangram_A_2_b.xml whose contents is

<svg version="1.1" xmlns="http://www.w3.org/2000/svg">

<path d="M 90 10 L 50 50 L 50 10 z" fill="red"/>

<path d="M 130 50 L 130 90 L 90 90 z" fill="green"/>

<path d="M 50 50 L 90 10 L 90 50 L 70 70 z" fill="magenta"/>

<path d="M 10 90 L 10 50 L 50 50 L 70 70 L 50 90 z" fill="purple"/>

<path d="M 70 110 L 70 130 L 50 130 L 50 90 z" fill="yellow"/>

<path d="M 90 50 L 130 50 L 70 110 L 50 90 z" fill="olive"/>

<path d="M 90 90 L 90 130 L 70 130 L 70 110 z" fill="blue"/>

</svg>

and which displays as follows.

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3. First task (4 marks)

You have to check that the pieces represented in an .xml file satisfy our constraints. So you have to check

that each piece is convex, and if it represents a polygon with n sides (n ≥ 3) then the representation consists

of an enumeration of the n vertices, either clockwise or anticlockwise. Here is the expected behaviour of your

program.

$ python3

...

>>> from tangram import *

>>> file = open('pieces_A.xml')

>>> coloured_pieces = available_coloured_pieces(file)

>>> are_valid(coloured_pieces)

True

>>> file = open('pieces_AA.xml')

>>> coloured_pieces = available_coloured_pieces(file)

>>> are_valid(coloured_pieces)

True

>>> file = open('incorrect_pieces_1.xml')

>>> coloured_pieces = available_coloured_pieces(file)

>>> are_valid(coloured_pieces)

False

>>> file = open('incorrect_pieces_2.xml')

>>> coloured_pieces = available_coloured_pieces(file)

>>> are_valid(coloured_pieces)

False

>>> file = open('incorrect_pieces_3.xml')

>>> coloured_pieces = available_coloured_pieces(file)

>>> are_valid(coloured_pieces)

False

>>> file = open('incorrect_pieces_4.xml')

>>> coloured_pieces = available_coloured_pieces(file)

>>> are_valid(coloured_pieces)

False

Note that the function are_valid() does not print out True or False, but returns True or False.

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4. Second task (4 marks)

You have to check whether the sets of pieces represented in two .xml files are identical, allowing for pieces to

be flipped over and allowing for different orientations. Here is the expected behaviour of your program.

$ python3

...

>>> from tangram import *

>>> file = open('pieces_A.xml')

>>> coloured_pieces_1 = available_coloured_pieces(file)

>>> file = open('pieces_AA.xml')

>>> coloured_pieces_2 = available_coloured_pieces(file)

>>> are_identical_sets_of_coloured_pieces(coloured_pieces_1, coloured_pieces_2)

True

>>> file = open('shape_A_1.xml')

>>> coloured_pieces_2 = available_coloured_pieces(file)

>>> are_identical_sets_of_coloured_pieces(coloured_pieces_1, coloured_pieces_2)

False

Note that the function identical_sets_of_coloured_pieces() does not print out True or False, but returns

True or False.

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5. Third task (5 marks)

You have to check whether the pieces represented in an .xml file are a solution to a tangram puzzle represented

in another .xml file. Here is the expected behaviour of your program.

$ python3

...

>>> from tangram import *

>>> file = open('shape_A_1.xml')

>>> shape = available_coloured_pieces(file)

>>> file = open('tangram_A_1_a.xml')

>>> tangram = available_coloured_pieces(file)

>>> is_solution(tangram, shape)

True

>>> file = open('tangram_A_2_a.xml')

>>> tangram = available_coloured_pieces(file)

>>> is_solution(tangram, shape)

False

Note that the function is_solution() does not print out True or False, but returns True or False.


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