Arrays vs Other Data Structures When to Choose Arrays in DSA Rust - Interactive Comparison Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare a fixed-size array of 5 integers in Rust.

DSA Rust

let numbers: [i32; 5] = [1];

Drag options to blanks, or click blank then click option'

A[1, 2, 3, 4, 5]

B{1, 2, 3, 4, 5}

C(1, 2, 3, 4, 5)

D<1, 2, 3, 4, 5>

Attempts:

3 left

💡 Hint

Common Mistakes

Using parentheses instead of square brackets.

Using curly braces or angle brackets which are invalid for arrays.

In Rust, arrays are declared using square brackets with elements inside, like [1, 2, 3, 4, 5].

2fill in blank

medium

Complete the code to access the third element of the array named 'values'.

DSA Rust

let third = values[1];

Drag options to blanks, or click blank then click option'

A[2]

B<2>

C{2}

D(2)

Attempts:

3 left

💡 Hint

Common Mistakes

Using parentheses or curly braces instead of square brackets.

Using index 3 instead of 2 for the third element.

Array elements are accessed using square brackets with zero-based indexing, so the third element is at index 2.

3fill in blank

hard

Fix the error in the code to create a vector with initial elements 10, 20, 30.

DSA Rust

let mut vec = Vec::new();
vec.[1](10);
vec.[1](20);
vec.[1](30);

Drag options to blanks, or click blank then click option'

Ainsert

Bappend

Cadd

Dpush

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'append' which expects another vector, not a single element.

Using 'insert' without specifying index.

Using 'add' which is not a vector method.

To add elements to a vector in Rust, use the push method.

4fill in blank

hard

Fill both blanks to create a vector from an array and then get its length.

DSA Rust

let arr = [1, 2, 3, 4];
let vec = Vec::[1](&arr);
let len = vec.[2]();

Drag options to blanks, or click blank then click option'

Afrom

Bnew

Clen

Dlength

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'new' instead of 'from' to create vector from array.

Using 'length' instead of 'len' method.

Use Vec::from to create a vector from an array, and len() to get its length.

5fill in blank

hard

Fill all three blanks to filter even numbers from a vector and collect them into a new vector.

DSA Rust

let numbers = vec![1, 2, 3, 4, 5, 6];
let evens: Vec<i32> = numbers.iter()
    .[1](|&x| x [2] 2 == 0)
    .[3]();

Drag options to blanks, or click blank then click option'

Afilter

B%

Ccollect

Dmap

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'map' instead of 'filter' which transforms elements.

Using '==' instead of '%' for checking evenness.

Forgetting to collect the iterator into a vector.

Use filter to keep only even numbers, % for modulo operation, and collect() to gather results into a vector.

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