Arrays vs Other Data Structures When to Choose Arrays in DSA Rust - Build Both Approaches

Arrays vs Other Data Structures: When to Choose Arrays

📖 Scenario: You are helping a small library organize its book inventory. The library wants to store a fixed list of book titles that rarely change. You will use an array to hold these book titles because arrays are simple and fast for fixed-size collections.

🎯 Goal: Build a Rust program that creates an array of book titles, sets a maximum allowed title length, filters books based on title length, and prints the filtered list.

📋 What You'll Learn

Create an array called books with exactly these titles: "The Hobbit", "1984", "Fahrenheit 451", "The Catcher in the Rye", "To Kill a Mockingbird"

Create a variable called max_length and set it to 15

Use a for loop with variable book to iterate over books and collect titles with length less than or equal to max_length into a vector called short_books

Print the short_books vector

💡 Why This Matters

🌍 Real World

Libraries, inventories, and simple fixed lists often use arrays for fast access and simple storage.

💼 Career

Understanding when to use arrays versus other data structures like vectors is important for writing efficient and clear Rust programs.

1

Create the array of book titles

Create an array called books with these exact titles: "The Hobbit", "1984", "Fahrenheit 451", "The Catcher in the Rye", "To Kill a Mockingbird"

DSA Rust

# Create the array books with the given titles
# Your code here

Hint

Use square brackets [] to create an array and separate titles with commas.

2

Set the maximum allowed book title length

Create a variable called max_length and set it to 15

DSA Rust

fn main() {
    let books = ["The Hobbit", "1984", "Fahrenheit 451", "The Catcher in the Rye", "To Kill a Mockingbird"];
    // Create max_length variable
    # Your code here
}

Hint

Use let max_length = 15; to create the variable.

3

Filter books by title length

Use a for loop with variable book to iterate over books and collect titles with length less than or equal to max_length into a vector called short_books

DSA Rust

fn main() {
    let books = ["The Hobbit", "1984", "Fahrenheit 451", "The Catcher in the Rye", "To Kill a Mockingbird"];
    let max_length = 15;
    // Create short_books vector and fill it with books having length <= max_length
    # Your code here
}

Hint

Use Vec::new() to create an empty vector. Use books.iter() to loop over the array. Use book.len() to get the length of each title.

4

Print the filtered list of short book titles

Print the short_books vector

DSA Rust

fn main() {
    let books = ["The Hobbit", "1984", "Fahrenheit 451", "The Catcher in the Rye", "To Kill a Mockingbird"];
    let max_length = 15;
    let mut short_books = Vec::new();
    for book in books.iter() {
        if book.len() <= max_length {
            short_books.push(*book);
        }
    }
    // Print short_books vector
    # Your code here
}

Hint

Use println!("{:?}", short_books); to print the vector in debug format.

Practice

1. Which of the following is the best reason to choose an array over other data structures like linked lists or hash maps?

easy

A. You want to store key-value pairs.

B. You need fast access to elements by index.

C. You need to frequently insert or delete elements in the middle.

D. You want to avoid fixed size limitations.

Solution

1. Step 1: Understand array access speed

   Arrays provide constant time access to elements by their index because elements are stored contiguously in memory.

2. Step 2: Compare with other data structures

   Linked lists and hash maps do not provide direct index access; linked lists require traversal, and hash maps use keys, not indexes.

3. Final Answer:

   You need fast access to elements by index. -> Option B

4. Quick Check:

   Fast index access = A [OK]

Hint: Arrays give quick element access by position [OK]

Common Mistakes:

• Confusing arrays with hash maps for key-value storage
• Thinking arrays are best for frequent insertions/deletions
• Ignoring fixed size limitation of arrays

2. Which of the following is the correct way to declare a fixed-size array of 5 integers in Rust?

easy

A. let arr: [i32; 5] = [0; 5];

B. let arr = [5; i32];

C. let arr = Vec<i32>::new(5);

D. let arr = array(5, 0);

Solution

1. Step 1: Recall Rust array syntax

   In Rust, fixed-size arrays are declared with type and size like [type; size].

2. Step 2: Check each option

   let arr: [i32; 5] = [0; 5]; correctly declares an array of 5 integers initialized to 0. let arr = [5; i32]; has wrong syntax, C creates a vector not an array, D is invalid Rust.

3. Final Answer:

   let arr: [i32; 5] = [0; 5]; -> Option A

4. Quick Check:

   Fixed-size array syntax = B [OK]

Hint: Use [type; size] syntax for fixed arrays in Rust [OK]

Common Mistakes:

• Using Vec instead of array for fixed size
• Wrong order of size and type in declaration
• Using non-Rust syntax for arrays

3. What will be the output of the following Rust code?

let arr = [10, 20, 30, 40, 50];
let slice = &arr[1..4];
println!("{:?}", slice);

medium

A. [20, 30, 40]

B. [30, 40, 50]

C. [20, 30, 40, 50]

D. [10, 20, 30]

Solution

1. Step 1: Understand Rust slice syntax

   The slice &arr[1..4] includes elements from index 1 up to but not including index 4.

2. Step 2: Identify elements in the slice

   Indexes 1, 2, 3 correspond to values 20, 30, and 40 respectively.

3. Final Answer:

   [20, 30, 40] -> Option A

4. Quick Check:

   Slice excludes end index = D [OK]

Hint: Slice includes start index, excludes end index [OK]

Common Mistakes:

• Including the end index element in the slice
• Confusing slice with full array
• Misreading index positions

4. Consider this Rust code snippet:

let mut arr = [1, 2, 3, 4, 5];
arr.push(6);

What is the error and how to fix it?

medium

A. The push method requires a reference; use &6.

B. The array is immutable; declare with let instead of let mut.

C. Arrays have no push method; use a Vec instead.

D. The array size is fixed; increase size to 6 in declaration.

Solution

1. Step 1: Identify array limitations in Rust

   Fixed-size arrays in Rust do not have a push method because their size cannot change.

2. Step 2: Suggest correct data structure

   Vectors (Vec) are growable arrays and support push.

3. Final Answer:

   Arrays have no push method; use a Vec instead. -> Option C

4. Quick Check:

   Fixed arrays no push = C [OK]

Hint: Use Vec for dynamic size, arrays are fixed [OK]

Common Mistakes:

• Trying to push on fixed-size arrays
• Confusing mutability with resizability
• Ignoring Rust's strict type and method rules

5. You need to store a large collection of numbers where you will frequently access elements by index and rarely add or remove elements. Which data structure should you choose in Rust and why?

hard

A. Use a hash map because it provides fast key-based access.

B. Use a Vec because it allows dynamic resizing and fast index access.

C. Use a linked list because it allows easy insertion and deletion anywhere.

D. Use a fixed-size array because it provides fast index access and fixed memory layout.

Solution

1. Step 1: Analyze access and modification needs

   Frequent index access requires fast, constant-time access. Rare modifications mean fixed size is acceptable.

2. Step 2: Compare arrays and vectors

   Fixed-size arrays have faster access and less overhead than vectors but cannot resize. Since additions/removals are rare, fixed size is fine.

3. Step 3: Exclude other structures

   Linked lists have slow index access; hash maps are for key-value, not index-based access.

4. Final Answer:

   Use a fixed-size array because it provides fast index access and fixed memory layout. -> Option D

5. Quick Check:

   Fast access + rare changes = fixed array [OK]

Hint: Fixed arrays excel with fast access and stable size [OK]

Common Mistakes:

• Choosing Vec when fixed size suffices
• Using linked list for index access
• Confusing hash map keys with indexes