Problem Set 5

It's time to put your skills to the test. This problem set focuses on using built-in methods, most notable of the String class. It is also your first introduction to methods that accept parameters and return values. The main method is declared, but it is up to you to implement. Write your code for each exercise in the corresponding method. Make sure you test your code thoroughly.

Getting Started

To get started, create a GitHub repository to store your code. When you're finished, clone my skeleton to get all of the starter code and instructions. Setup a remote to push your code to your repository instead of mine.

Setup

1. Login to your GitHub account and create a new repository named pset-5.
2. In the terminal, navigate to your APCSA directory on the Desktop.

$ cd ~/Desktop/APCSA

3. Clone my skeleton repository into a directory named pset-5.

$ git clone git@github.com:ap-java-ucvts/pset-5-skeleton.git pset-5

4. Change into your newly created pset-5 directory.

$ cd pset-5

5. Overwrite the remote, which originally points at my skeleton repository.

$ git remote rename origin upstream

6. Add a new remote that points at your pset-5 repository. Replace YOUR-USERNAME with your actual username.

$ git remote add origin git@github.com:YOUR-USERNAME/pset-5.git

7. Open up the ProblemSet5.java file in the text editor of your choice.

All of the method signatures are written for you, as is the main method. Please read each comment carefully, as they are designed to point you in the right direction for the associated exercise.

Exercises

The specifications for each exercise are outlined below. Your job is to write lines of code to produce answers to my questions. Each exercise requires that you ask the user to enter one or more values. Your code must meet the requirements set forth in this section.

Work through these exercises on your own. Experiment, make mistakes, ask questions, and fix your mistakes. It's the only way to get good at programming.

Exercise 1

Given two strings, return a new string built by surrounding in with the first and last two characters of out. Return in unchanged if any of the following requirements are not met.

• in must not be null.
• out must not be null.
• out must be exactly 4 characters.

surroundMe("cde", "abfg") → abcdefg
surroundMe(null, "####")  → null
surroundMe("abc", null)   → "abc"
surroundMe("abc", "123")  → "abc"

Remember, your code will need to handle atypical cases, too. null values, empty Strings, and special characters (including escape sequences) are all valid inputs.

Exercise 2

Given a string and an integer, return a new string that represents the first and last n characters of text. Return text unchanged if any of the following requirements are not met.

• text must not be null.
• text must be between 1 and 10 characters (inclusive).
• n must be a positive integer between 1 and the length of text (inclusive).

endsMeet("abcdefg", 2) → "abcdefg"
endsMeet(null, 2)      → null
endsMeet("", 2)        → ""
endsMeet("abc", -1)    → "abc"

Remember, your code will need to handle atypical cases, too. null values, empty Strings, and special characters (including escape sequences) are all valid inputs.

Exercise 3

Given a string, return a new string using the middle three characters of text. Return text unchanged if any of the following requirements are not met.

• text must not be null.
• text must have an odd length of at least 3 characters.

middleMan("abcdefg") → "cde"
middleMan(null)      → null
middleMan("12")      → "12"
middleMan("a")       → "a"

Remember, your code will need to handle atypical cases, too. null values, empty Strings, and special characters (including escape sequences) are all valid inputs.

Exercise 4

Given two strings, determine whether or not target is equivalent to the middle three characters of text. Return false if any of the following requirements are not met.

• text must not be null.
• text must have an odd length of at least 3 characters.
• target must not be null.
• target must be exactly 3 characters.

isCentered("abcdefg", "cde") → true
isCentered("abcdefg", "abc") → false
isCentered(null, "abc")      → false
isCentered("abcd", "abc")    → false
isCentered("abc", null)      → false
isCentered("abcdefg", "cd")  → false

Remember, your code will need to handle atypical cases, too. null values, empty Strings, and special characters (including escape sequences) are all valid inputs.

Exercise 5

Given a string and a character, compute the number of words that end in suffix. Return -1 if any of the following requirements are not met.

• text must not be null.
• suffix must be a character in the English alphabet.

Treat the suffix case-sensitively. A word is defined as a sequence of characters that starts and ends in a single space. The only exception to this is if the word is either the first or last word in the string. There will never be more than one consecutive space in the string, and no other whitespace characters will appear in the string.

countMe("I am an example sentence", 'e') → 2
countMe(null, 'a')                       → -1
countMe("abc$ def$", '$')                → -1

Remember, your code will need to handle atypical cases, too. null values, empty Strings, and special characters (including escape sequences) are all valid inputs.

Exercise 6

Given a string, compute the number of triplets in text. Return -1 if any of the following requirements are not met.

• text must not be null.

A triplet is defined as the appearance of three consecutive characters (i.e., "aaa"). Triplets are case-sensitive.

triplets("aaabbbccc") → 3
triplets("aaaa")      → 2
triplets("abc")       → 0
triplets(null)        → -1

Remember, your code will need to handle atypical cases, too. null values, empty Strings, and special characters (including escape sequences) are all valid inputs.

Exercise 7

Given a string, compute the sum of the digits in text. Return -1 if any of the following requirements are not met.

• text must not be null.

Ignore characters that are not digits. All digits are assumed to be positive.

addMe("123 abc 123") → 12
addMe("abcdefghijk") → 0
addMe(null)          → -1

Remember, your code will need to handle atypical cases, too. null values, empty Strings, and special characters (including escape sequences) are all valid inputs.

Exercise 8

Given a string, compute the length of the longest sequence. Return -1 if any of the following requirements are not met.

• text must not be null.

A sequence is defined as one or more consecutive characters. These characters must be identical, and are case-sensitive.

sequence("abbcccdddd") → 4
sequence("aAabBbBb")   → 1
sequence("")           → 0
sequence(null)         → -1

Remember, your code will need to handle atypical cases, too. null values, empty Strings, and special characters (including escape sequences) are all valid inputs.

Exercise 9

Given two strings, return a new string built by intertwining each of the characters of a and b. Return null if any of the following requirements are not met.

• a must not be null.
• b must not be null.

sequence("aceg", "bdfh") → "abcdefgh"
sequence("abc", "12345") → a1b2c345"
sequence(null, "abcd")   → null
sequence("abcd", null)   → null
sequence(null, null)     → null

Remember, your code will need to handle atypical cases, too. null values, empty Strings, and special characters (including escape sequences) are all valid inputs.

Exercise 10

Given a string, determine whether or not it is a palindrome. Return false if any of the following requirements are not met.

• text must not be null.

A palindrome is case-sensitive. Use of the StringBuilder or StringBuffer classes is strictly prohibited.

isPalindrome("racecar") → true
isPalindrome("Madam")   → false
isPalindrome(null))     → false

Remember, your code will need to handle atypical cases, too. null values, empty Strings, and special characters (including escape sequences) are all valid inputs.

Deadline

Please read very carefully. Historically, most students lose points on problem sets for simply failing to read the instructions and requirements.

• November 6, 2019, at 11:59pm.

If you submit your problem set at midnight (i.e., November 7, 2019, at 12:00am), it is considered late!

Submission Requirements

• Your code must compile. Code that fails to meet this minimum requirement will not be accepted.
• There must be at least 10 unique commits to your repository.
• Your code must meet each requirement outlined in the Exercises section.
• Your code must adhere to the course style guidelines.

Happy coding!