Why Sorting Matters and How It Unlocks Other Algorithms in DSA Rust - Test Your Knowledge

Practice - 5 Tasks

1fill in blank

easy

Complete the code to sort the vector in ascending order.

DSA Rust

let mut numbers = vec![5, 3, 8, 1];
numbers.[1]();

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

Apop

Breverse

Cpush

Dsort

Attempts:

3 left

💡 Hint

Common Mistakes

Using reverse() which flips the order but does not sort.

Using push() or pop() which add or remove elements.

The sort() method sorts the vector in ascending order.

2fill in blank

medium

Complete the code to find if the number 4 exists in the sorted vector using binary search.

DSA Rust

let numbers = vec![1, 3, 5, 7, 9];
let result = numbers.binary_search(&[1]);

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A2

B7

C4

D5

Attempts:

3 left

💡 Hint

Common Mistakes

Choosing a number not intended to search for.

Confusing the index with the value.

Binary search looks for the value 4 in the sorted vector.

3fill in blank

hard

Fix the error in the code to sort a vector of strings alphabetically.

DSA Rust

let mut words = vec!["pear", "apple", "orange"];
words.[1]();

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Asort

Bsort_by_key

Csort_unstable

Dreverse

Attempts:

3 left

💡 Hint

Common Mistakes

Using reverse() which only reverses order.

Using sort_by_key without a key function.

The sort() method sorts strings alphabetically in place.

4fill in blank

hard

Fill both blanks to create a vector of squares for numbers greater than 3.

DSA Rust

let numbers = vec![1, 2, 3, 4, 5];
let squares: Vec<_> = numbers.iter().filter(|&&x| x [1] 3).map(|&x| x[2]x).collect();

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A>

B*

C<

D+

Attempts:

3 left

💡 Hint

Common Mistakes

Using less than operator which filters wrong numbers.

Using addition instead of multiplication.

Filter numbers greater than 3 and square them using multiplication.

5fill in blank

hard

Fill both blanks to create a dictionary mapping words to their lengths for words longer than 4 characters.

DSA Rust

let words = vec!["tree", "house", "car", "elephant"];
let word_lengths: std::collections::HashMap<_, _> = words.iter().filter(|&&word| word.len() [1] 4).map(|&word| (word[2], word.len(),)).collect();

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A>

B.to_string()

C,

D<

Attempts:

3 left

💡 Hint

Common Mistakes

Using less than operator which filters wrong words.

Forgetting to convert &str to String.

Missing comma between tuple elements.

Filter words longer than 4, convert word to String, and map to (word, length) pairs separated by a comma.

Practice

1. Why is sorting an important step before applying many algorithms in data processing?

easy

A. It removes duplicate data automatically

B. It encrypts data for security

C. It organizes data to make searching and comparisons faster

D. It compresses data to save space

Solution

1. Step 1: Understand sorting's role in data organization

   Sorting arranges data in order, which helps algorithms work efficiently by reducing complexity.

2. Step 2: Connect sorting to faster searching and comparisons

   When data is sorted, algorithms like binary search can quickly find elements, improving speed.

3. Final Answer:

   It organizes data to make searching and comparisons faster -> Option C

4. Quick Check:

   Sorting improves search speed = B [OK]

Hint: Sorting arranges data to speed up searches and comparisons [OK]

Common Mistakes:

• Thinking sorting removes duplicates automatically
• Confusing sorting with encryption or compression

2. Which of the following is the correct Rust syntax to sort a mutable vector nums in ascending order?

easy

A. nums.sort();

B. nums.sorted();

C. sort(nums);

D. nums.sort_by_desc();

Solution

1. Step 1: Identify Rust's method to sort vectors

   Rust's standard library provides the sort() method for mutable vectors to sort in ascending order.

2. Step 2: Check each option's correctness

   nums.sort(); uses nums.sort(); which is correct. nums.sorted(); uses a non-existent method sorted(). sort(nums); is a function call not valid in Rust. nums.sort_by_desc(); sorts descending, which is not asked.

3. Final Answer:

   nums.sort(); -> Option A

4. Quick Check:

   Rust vector sort method = A [OK]

Hint: Use vec.sort() to sort mutable vectors ascending [OK]

Common Mistakes:

• Using non-existent methods like sorted()
• Trying to call sort as a free function
• Confusing ascending and descending sort methods

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

let mut nums = vec![3, 1, 4, 1, 5];
nums.sort();
println!("{:?}", nums);

medium

A. Compilation error

B. [5, 4, 3, 1, 1]

C. [3, 1, 4, 1, 5]

D. [1, 1, 3, 4, 5]

Solution

1. Step 1: Understand the initial vector and sorting

   The vector nums starts as [3, 1, 4, 1, 5]. Calling nums.sort() sorts it in ascending order.

2. Step 2: Determine the sorted vector

   Sorting gives [1, 1, 3, 4, 5]. The print statement outputs this vector.

3. Final Answer:

   [1, 1, 3, 4, 5] -> Option D

4. Quick Check:

   Sorted vector output = A [OK]

Hint: Sorting arranges numbers from smallest to largest [OK]

Common Mistakes:

• Confusing ascending with descending order
• Expecting original order after sort
• Thinking sort causes compile errors

4. The following Rust code tries to sort a vector but causes a compilation error. What is the error and how to fix it?

let nums = vec![2, 3, 1];
nums.sort();

medium

A. Error: Missing semicolon; fix by adding semicolon after vector declaration

B. Error: Cannot borrow immutable variable as mutable; fix by declaring nums as mutable

C. Error: sort() method does not exist for vectors; fix by importing a crate

D. No error; code runs fine

Solution

1. Step 1: Identify the variable mutability

   The vector nums is declared immutable with let. The sort() method requires a mutable reference.

2. Step 2: Fix by making the vector mutable

   Change declaration to let mut nums = vec![2, 3, 1]; to allow sorting.

3. Final Answer:

   Error: Cannot borrow immutable variable as mutable; fix by declaring nums as mutable -> Option B

4. Quick Check:

   Mutable vector needed for sort() = C [OK]

Hint: Declare vector mutable with mut before sorting [OK]

Common Mistakes:

• Trying to sort immutable vectors
• Thinking sort() needs external crates
• Ignoring Rust's mutability rules

5. You have a list of student scores: vec![88, 95, 70, 100, 85]. You want to find the median score efficiently. Which approach best uses sorting to unlock this algorithm?

hard

A. Sort the scores and pick the middle element after sorting

B. Sum all scores and divide by the number of scores

C. Find the maximum and minimum scores and average them

D. Shuffle the scores randomly and pick any element

Solution

1. Step 1: Understand median calculation

   The median is the middle value in a sorted list, so sorting is necessary to find it correctly.

2. Step 2: Apply sorting to find the median

   Sort the vector to get [70, 85, 88, 95, 100]. The middle element (3rd) is 88, the median.

3. Final Answer:

   Sort the scores and pick the middle element after sorting -> Option A

4. Quick Check:

   Median requires sorted data = D [OK]

Hint: Sort first, then pick middle for median [OK]

Common Mistakes:

• Using average instead of median
• Ignoring sorting before median calculation
• Picking random elements without sorting