代写program编程设计、Python留学生程序代做

日期：2021-03-03 10:15

Lab 2

Strings, Loops, and Ciphers

In lecture, we briefly discussed an example of using a cipher (where a message is put

into secret writing by encoding each letter to be represented by something else).

Step 1: Create your own cipher

Take out a pen and paper to brainstorm some ideas, your goal is to create your own

cipher that uses a one-to-one mapping of each letter of the alphabet to something else

(either a number, or another letter, etc.) in order to encode a message in a way that is

not easily decipherable.

However, you may create no more than three rules (so, create 1, 2 or 3 rules) for your

cipher. These rules are single statements that are used to transform the message.

Additionally, you must not change or add words or change word order and all

punctuation must be retained unaltered. Basically, all you are allowed to change are the

letters.

Here is an example of a cipher we could create:

Rule 1. The characters are divided into two groups: (1) characters that have an

enclosed area in uppercase and (2) characters that do not have an enclosed area in

uppercase.

Rule 2. Sort the two groups alphabetically, with group 1 first and then group 2.

Rule 3. Number the sorted list using 1-indexing and use the corresponding number for

each character as its code.

Here is the application of the cipher:

Applying Rule 1:

Group 1: {A, B, D, O, P, Q, R }

Group 2: {C, E, F, G, H, I, J, K, L, M, N, S, T, U, V, W, X, Y, Z}

Applying Rule 2:

A, B, D, O, P, Q, R, C, E, F, G, H, I, J, K, L, M, N, S, T, U, V, W, X, Y, Z

Applying Rule 3 will produce a 1-to-1 mapping table:

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26

A B D O P Q R C E F G H I J K L M N S T U V W X Y Z

This will translate the message:

"We drove to the gym and swam in the pool."

To:

23_9 3_7_4_22_9 20_4 20_12_9 11_25_17 1_18_3 19_23_1_17 13_18

20_12_9 5_4_4_16

If you were to try to make each character encode to another randomly selected

character, it would require 26 rules, and that would violate the above requirements. That

is, you must find a way to treat each character to a transformation using the same set of

rules. Any special characters, such as whitespace or punctuation, should be left as is.

Although for readability's sake like in the cipher above, we had to indicate character

breaks with a _ symbol, and tripled the space between each word.

Step 2: Write an encoded message

Take a piece of paper (or anything you can scribble/type on) and encode a few

messages using your method. You don’t need to hand this in, but it will help you in the

next step as you will have something to refer to when implementing your cipher.

Step 3: Write an encoding program

Open up a new file called cipher.py and write a function that takes in an English

sentence and encodes it according to your personal encoding algorithm. The function

should have a type contract str -> str, that is it takes in a string and returns an encoded

string.

This file should have the rules you came up with in step 1 as comments at the top of the

file or as a multi-line string.

Submit cipher.py to MarkUs once you are done.

Step 4 (Optional): Write a decoding program

Optionally, write another function that decodes an encoded string. That is, given an

encoded string output from the function you wrote for step 3, this function should

decipher it and return the original string before it was encoded.

If you decide to do this step, simply submit it along with the code in step 3, the TAs will

see that you have an additional function when marking.