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COMP9021 program Assignment

创建日期：2024-07-31 16:46:49

所属分类：计算机computer science

标签： COMP9021

program Assignment

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Assignment

COMP9021

1. General matters

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

? let you design solutions to simple problems;

? let you implement these solutions in the form of short Python programs;

? practice the use of arithmetic computations, tests, repetitions, lists, tuples, dictionaries, deques, reading

from files.

1.2. Submission. Your programs will be stored in a number of files, with one file per exercise, of the appropriate

name. After you have developed and tested your programs, upload your files using Ed. Assignments can be

submitted more than once: the last version is marked. Your assignment is due by September 2, 11:59pm.

1.3. Assessment. Each of the 4 exercises is worth 2.5 marks. For all exercises, the automarking script will let

each of your programs run for 30 seconds. Still you should not take advantage of this and strive for a solution

that gives an immediate output for “reasonable” inputs.

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

and 10 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.

2. Rain

Write a program, stored in a file named rain.py, that performs the following task.

? The program prompts the user to input a file name. If there is no file with that name in the working

directory, then the program outputs an (arbitrary) error message and exits.

? The program prompts the user to input a nonnegative integer. If the input is not a nonnegative integer,

then the program outputs an (arbitrary) error message and exits.

? The contents of the file consists of some number of lines, each line being a sequence of the same number

of nonnegative integers separated by at least one space, with possibly spaces before and after the first

and last number, respectively. These numbers represent the height in centimetres of a block with a

square base of 10 square centimetres. For instance, the contents of the file land.txt can be represented

2 2 2 2 2

1 3 4 3 2

2 3 5 3 2

2 4 1 1 2

and would represent a land covering an area of 50 centimetres by 40 centimetres, with a block of height 2

centimetres in each corner, etc. The number input by the user represents a quantity of rain in decilitres,

to be poured down on the land.

? The program outputs the height in centimetres, with a precision of 2 digits after the decimal point, that

is reached by the water.

Here is a possible interaction:

$ cat land.txt

2 2 2 2 2

1 3 4 3 2

2 3 5 3 2

2 4 1 1 2

$ python3 rain.py

Which data file do you want to use? land.txt

How many decilitres of water do you want to pour down? 1

The water rises to 1.33 centimetres.

$ $ python3 rain.py

Which data file do you want to use? $ land.txt

How many decilitres of water do you want to pour down? 33

The water rises to 4.00 centimetres.

$ $ python3 rain.py

Which data file do you want to use? $ land.txt

How many decilitres of water do you want to pour down? 50

The water rises to 4.89 centimetres.

You can assume that the contents of any test file is as expected, you do not have to check that it is as

expected.

3. Superpowers

Write a program, stored in a file named superpower.py, that does the following.

? The program prompts the user for an arbitrary number of (positive or negative) integers, all provided

on one line and separated by at least one space, with possibly extra spaces anywhere. The user can

input no integer at all. If the input is incorrect, then the program outputs an error message and exits.

These integers are meant to represent the superpower of a bunch of heroes (positive power is good, all

the better that it is larger; negative power is bad, all the worse that it is smaller).

? Then the program prompts the user for a nonnegative integer (possibly equal to 0), nb_of_switches, at

most equal to the number of integers previously input (the number of heroes). If the input is incorrect,

then the program outputs another error message and exits. This number is meant to represent the

number of switches (multiplication by -1) to the power of some heroes; for instance, a hero with positive

power 7 can see its power switched to -7, and a hero with negative power -5 can see its power switched

to 5.

? First, the program determines the maximum overall power that can be achieved by switching the power

of nb_of_switches many heroes, a given hero seeing its power being switched an arbitrary number

of times (not switched at all, or switched once, or switched more than once). For instance, with the

sequence (4, -3, 1, 2, -7) and nb_of_switches set to 3, the maximum overall power that can be achieved

is 15; this can be done by switching -3, 1 and -7 once: 4 + 3 ? 1 + 2 + 7 = 15. For another example,

with the sequence (-7, 1, 2, 3, 4) and nb_of_switches set to 5, the maximum overall power that can

be achieved is 17; this can be done by switching -7 once, 1 twice, and 3 twice: 7 + 1 + 2 + 3 + 4 = 17.

? Second, the program determines the maximum overall power that can be achieved by switching the

power of nb_of_switches many heroes, a given hero seeing its power being switched at most once (not

switched at all, or switched once). For instance, with the sequence (4, -3, 1, 2, -7) and nb_of_switches

set to 3, the maximum overall power that can be achieved is 15, as previously described. For another

example, with the sequence (-7, 1, 2, 3, 4) and nb_of_switches set to 5, the maximum overall power

that can be achieved is -3, as each power has to be switched: 7 ? 1 ? 2 ? 3 ? 4 = ?3.

? Third, the program determines the maximum overall power that can be achieved by switching the power

of nb_of_switches many consecutive heroes (note that first and last heroes are not consecutive, the

heroes are aligned on a line). For instance, with the sequence (4, -3, 1, 2, -7) and nb_of_switches set

to 3, the maximum overall power that can be achieved is 5; this can be done by switching the power

of the last 3 heroes: 4 ? 3 ? 1 ? 2 + 7 = 5. For another example, with the sequence (-7, 1, 2, 3, 4)

and nb_of_switches set to 5, the maximum overall power that can be achieved is -3, as previously

described.

? Fourth, the program determines the maximum overall power that can be achieved by switching the

power of arbitrarily many (possibly none) consecutive heroes. For instance, with the sequence (4, -3, 1,

2, -7), the maximum overall power that can be achieved is 17; this can be done by switching the power

of the last 4 heroes: 4 + 3 ? 1 ? 2 + 7 = 11. For another example, with the sequence (-7, 1, 2, 3, 4), the

maximum overall power that can be achieved is 17; this can be done by switching the power of the first

hero: 7 + 1 + 2 + 3 + 4 = 17.

Here is a possible interaction:

$ python3 superpower.py

Please input the heroes' powers: 3 5 8.5

Sorry, these are not valid power values.

$ python3 superpower.py

Please input the heroes' powers: 3 5 8

Please input the number of power flips: 4

Sorry, this is not a valid number of power flips.

$ python3 superpower.py

Please input the heroes' powers: 4 -3 1 2 -7

Please input the number of power flips: 3

Possibly flipping the power of the same hero many times, the greatest achievable power is 15.

Flipping the power of the same hero at most once, the greatest achievable power is 15.

Flipping the power of nb_of_flips many consecutive heroes, the greatest achievable power is 5.

Flipping the power of arbitrarily many consecutive heroes, the greatest achievable power is 11.

$ python3 superpower.py

Please input the heroes' powers: -7 1 2 3 4

Please input the number of power flips: 5

Possibly flipping the power of the same hero many times, the greatest achievable power is 17.

Flipping the power of the same hero at most once, the greatest achievable power is -3.

Flipping the power of nb_of_flips many consecutive heroes, the greatest achievable power is -3.

Flipping the power of arbitrarily many consecutive heroes, the greatest achievable power is 17.

$ python3 superpower.py

Please input the heroes' powers: 1 2 3 4 5

Please input the number of power flips: 2

Possibly flipping the power of the same hero many times, the greatest achievable power is 15.

Flipping the power of the same hero at most once, the greatest achievable power is 9.

Flipping the power of nb_of_flips many consecutive heroes, the greatest achievable power is 9.

Flipping the power of arbitrarily many consecutive heroes, the greatest achievable power is 15.

4. Cable car

Consider the following picture of the pillars and cable that provide the structure for a cable car. Successive

pillars are equidistant. The height of each pillar is indicated above it. Continuous pillars make up for a good

ride if the slope does not change over the corresponding section. Here the longest good ride is between the

pillar of height 25 and the pillar of height 28; it is depicted in blue. It has a length of 3 (units, whatever it is).

14 15

25 26 27 28

30 31

If one gets rid of the black pillars and keeps only the remaining (red) ones, then one can use use the latter

and create a new structure (with successive pillars being equidistant) which makes up for a perfect ride, that

is, good from first to last pillar:

It is the longest perfect ride one can obtain this way; so 5, the number of black pillars, is the minimal number

of pillars to remove to build a perfect ride from the rest.

Write a program, stored in a file named cable_car.py, that performs the following task.

? The program prompts the user to input a file name. If there is no file with that name in the working

directory, then the program outputs an error message and exits.

? The contents of the file should consist of a strictly increasing sequence of at least two strictly positive

integers. Consecutive numbers are separated by at least one space, and there can be extra spaces,

including empty lines, anywhere. If that is not the case then the program outputs another error message

and exits.

? These numbers are meant to represent the heights of pillars to build a cable car structure. The program

then outputs:

– whether or not this structure makes up for a perfect ride;

– the length of the longest good ride;

– how many pillars to remove to build a perfect ride from the remaining ones.

Here is a possible interaction:

$ python3 cable_car.py

Please enter the name of the file you want to get data from: non_existent_file.txt

Sorry, there is no such file.

$ cat cable_car_wrong_1.txt

$ python3 cable_car.py

Please enter the name of the file you want to get data from: cable_car_wrong_1.txt