Practice with Strings

Homework: Rot 13 Encryption

Created By: Geoffrey Challen

/ Version: 2020.9.0

Encryption is an ancient practice of trying to conceal information by scrambling it. Modern encryption techniques are incredibly strong and mathematically sound. But in the past, simpler and more primitive methods were used.

Let's implement a form of encryption known as a Caesar Cipher, sometimes also known as Rot-13 encryption. (Rot for rotation, and 13 for one amount that you might rotate.) Here is how it works. Given a String and an amount to rotate, we replace each character in the String with a new character determined by rotating the original character in a given array. For example, given the String array "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz ", "ABC" rotated 3 would be "DEF", and rotated -1 would be " AB". (Note the space at the end of the character array.)

Declare and implement a function called encrypt that, given a String and an Int amount, returns the passed String "encrypted" by rotating it the given amount. ("Encrypted" is in scare quotes because this is not by any means a strong method of encryption!) If the passed String is null you should return null. Note that rotation may be negative, which will require some additional care.

Homework: Rot 13 Encryption

Created By: Geoffrey Challen

/ Version: 2020.9.0

Encryption is an ancient practice of trying to conceal information by scrambling it. Modern encryption techniques are incredibly strong and mathematically sound. But in the past, simpler and more primitive methods were used.

Let's implement a form of encryption known as a Caesar Cipher, sometimes also known as Rot-13 encryption. (Rot for rotation, and 13 for one amount that you might rotate.) Here is how it works. Given a String and an amount to rotate, we replace each character in the String with a new character determined by rotating the original character in a given array. For example, given the String array "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz ", "ABC" rotated 3 would be "DEF", and rotated -1 would be " AB". (Note the space at the end of the character array.)

Declare and implement a function called encrypt that, given a String and an Int amount, returns the passed String "encrypted" by rotating it the given amount. ("Encrypted" is in scare quotes because this is not by any means a strong method of encryption!) If the passed String is null you should return null. Note that rotation may be negative, which will require some additional care.

Created By: Geoffrey Challen

/ Version: 2020.9.1

This problem combines Strings, functions, and arrays. Super fun!

Write a function called rotateRight that takes a nullable String as its first argument and a non-negative Int as its second argument and rotates the String by the given number of characters. Here's what we mean by rotate:

• CS125 rotated right by 1 becomes 5CS12
• CS125 rotated right by 2 becomes 25CS1
• CS125 rotated right by 3 becomes 125CS
• CS125 rotated right by 4 becomes S125C
• CS125 rotated right by 5 becomes CS125
• CS125 rotated right by 8 becomes 125CS

And so on. Notice how characters rotated off the right end of the String wrap around to the left.

This problem is tricky! Here are a few hints:

1. You will want to use the remainder operator to perform modular arithmetic.
2. You will probably want to convert the String to an array of characters before you begin.
3. You can convert an array of characters characters back into a String like this: String(characters).
4. You can also solve this problem quite elegantly using substring.

If the passed String argument is null, you should return null. Good luck and have fun!