Homework 4: Rust Homework

This is an individual assignment. You must work on this homework alone.

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Introduction

This homework introduces you to fundamental Rust programming concepts, including:

• basic data types (u32, i32, String, bool)
• vectors (Vec<T>)
• hash maps (HashMap<K, V>)
• defining structs and methods using impl
• Rust control flow: loops, branching, pattern matching
• writing and running Rust tests

You will complete two components:

1. A set of warm-up functions (Part 1)
2. A PhoneBook data structure (Part 2)

All code should be placed in src/lib.rs file.

Testing

Public tests are provided in: tests/public.rs

Run them with: cargo test --test public

You may add additional tests in: tests/student.rs

and run them using: cargo test --test student

Part 1 — Warm-up Functions

1. fib(n)

Return a vector containing the first n Fibonacci numbers.

Rust signature:

pub fn fib(n: u32) -> Vec<u32>

Examples:

fib(0) → []
fib(1) → [0]
fib(2) → [0, 1]
fib(3) → [0, 1, 1]
fib(10) → [0, 1, 1, 2, 3, 5, 8, 13, 21, 34]

Assume n ≥ 0.

2. is_palindrome(n)

Goal: Return true if the number reads the same forward and backward; otherwise return false.

Rust signature:

pub fn is_palindrome(n: u32) -> bool

You may convert the integer to a string for convenience.

Assume:

• n is non-negative
• `n has no leading zeros

3. nthmax(n, a)

Goal: Return the n-th largest value in the array a, or None if it does not exist. The largest value corresponds to n = 0.

Rust signature:

pub fn nthmax(n: usize, a: &[i32]) -> Option<i32>

Examples:

nthmax(0, [1,2,3,0]) → Some(3)
nthmax(1, [3,2,1,0]) → Some(2)
nthmax(2, [7,3,4,5]) → Some(4)
nthmax(5, [1,2,3])   → None

Assume n ≥ 0.

4. freq(s)

Goal: Return the character that appears most frequently in the string s. If s is empty, return the empty string.

Rust signature:

pub fn freq(s: &str) -> String

Assume there are no ties for most frequent character.

5. zip_hash(arr1, arr2)

Goal: Return a hash map where arr1[i] is mapped to arr2[i]. If the vectors differ in length, return None.

Rust signature:

pub fn zip_hash(
    keys: &[String],
    values: &[String]
) -> Option<std::collections::HashMap<String, String>>

Examples:

zip_hash([], []) → Some({})
zip_hash(["a"], ["b"]) → Some({"a" -> "b"})
zip_hash(["a"], ["b", "c"]) → None

6. hash_to_array(map)

Goal: Return a vector of (key, value) pairs from the hash map. Pairs must be ordered by sorted key order (or the order required by tests).

Rust signature:

pub fn hash_to_array(
    map: &std::collections::HashMap<String, String>
) -> Vec<(String, String)>

Part 2 - PhoneBook Struct

You will implement a PhoneBook type using a Rust struct and impl block.

A phone book records:

• a person's name
• their phone number (NNN-NNN-NNNN)
• whether the entry is listed or unlisted

You may choose any internal representation (e.g., one or multiple hash maps).

add(name, number, is_listed)

Goal: Add an entry to the phone book.

Rust signature:

pub fn add(&mut self, name: String, number: String, is_listed: bool) -> bool

Rules:

• If the name already exists, the add fails.
• If the phone number is not in NNN-NNN-NNNN format, the add fails.
• A number can be added as unlisted any number of times.
• A number can be added as listed only once.
• If a number already exists as listed, it may only be added again as unlisted.

Return true if added successfully; otherwise false.

lookup(name)

Goal: Return the phone number for name only if the entry is listed; otherwise return None.

Signature:

pub fn lookup(&self, name: &str) -> Option<String>

lookup_by_num(number)

Goal: Return the name associated with the phone number only if the entry is listed.

Signature:

pub fn lookup_by_num(&self, number: &str) -> Option<String>

names_by_ac(areacode)

Goal: Return all names whose phone numbers begin with areacode. This includes listed and unlisted entries.

Signature:

pub fn names_by_ac(&self, areacode: &str) -> Vec<String>

The returned vector does not need a specific sort order unless required by tests.

Good luck, and enjoy learning Rust!