Array Reversal Techniques in DSA Rust - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to reverse the array using the built-in method.

DSA Rust

let mut arr = [1, 2, 3, 4, 5];
arr.[1]();
println!("{:?}", arr);

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

Apop

Bpush

Creverse

Dsort

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'sort' which arranges elements in order, not reverses.

Using 'push' or 'pop' which are for vectors, not arrays.

The built-in method to reverse an array in Rust is 'reverse()'. It reverses the elements in place.

2fill in blank

medium

Complete the code to swap elements at positions i and j in the array.

DSA Rust

let mut arr = [10, 20, 30, 40];
let i = 0;
let j = 3;
arr.[1](i, j);
println!("{:?}", arr);

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

Asort

Breverse

Cclone

Dswap

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'reverse' which reverses the whole array, not swap two elements.

Using 'clone' which copies the array.

The 'swap' method exchanges elements at two indices in the array.

3fill in blank

hard

Fix the error in the loop to reverse the array manually.

DSA Rust

let mut arr = [1, 2, 3, 4, 5];
let n = arr.len();
for i in 0..n / 2 {
    arr.[1](i, n - i - 1);
}
println!("{:?}", arr);

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

Aswap

Breverse

Csort

Dpush

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'reverse' inside the loop which is incorrect.

Using 'push' which is not valid for arrays.

To reverse manually, swap elements from start and end moving towards the center using 'swap'.

4fill in blank

hard

Fill both blanks to create a reversed vector from the array.

DSA Rust

let arr = [1, 2, 3, 4];
let rev_vec: Vec<_> = arr.iter().[1]().[2]().collect();
println!("{:?}", rev_vec);

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

Arev

Bcloned

Ccopied

Dsorted

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'cloned' instead of 'copied' which works but is less efficient for Copy types.

Using 'sorted' which sorts instead of reversing.

First reverse the iterator with 'rev()', then copy elements with 'copied()' to get owned values for the vector.

5fill in blank

hard

Fill all three blanks to reverse the array using a for loop and temporary variable.

DSA Rust

let mut arr = [5, 6, 7, 8];
let n = arr.len();
for i in 0..n / 2 {
    let temp = arr[[1]];
    arr[[2]] = arr[[3]];
    arr[[3]] = temp;
}
println!("{:?}", arr);

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

Ai

Bn - i - 1

Cn - i

Di + 1

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'n - i' which is out of bounds.

Mixing up indices causing incorrect swaps.

Use 'i' for the first index, assign arr[i] = arr[n - i - 1], and arr[n - i - 1] = temp to swap manually.

Practice

1. What does reversing an array mean in simple terms?

easy

A. Changing the order of elements so the last becomes first and first becomes last

B. Sorting the array in ascending order

C. Removing duplicate elements from the array

D. Adding new elements to the end of the array

Solution

1. Step 1: Understand array reversal

   Reversing means flipping the order of elements so the last element comes first and the first element goes last.

2. Step 2: Compare with other options

   Sorting arranges elements by value, removing duplicates deletes repeats, and adding elements is insertion, not reversal.

3. Final Answer:

   Changing the order of elements so the last becomes first and first becomes last -> Option A

4. Quick Check:

   Reversal = Flip order [OK]

Hint: Reversal flips order, not sorting or adding [OK]

Common Mistakes:

• Confusing reversal with sorting
• Thinking reversal removes elements
• Mixing reversal with adding elements

2. Which of the following Rust code snippets correctly reverses a mutable array arr in place?

easy

A. arr = arr.reverse();

B. arr.reverse();

C. arr.reverse(&mut arr);

D. reverse(arr);

Solution

1. Step 1: Identify correct method usage

   In Rust, the reverse() method is called directly on a mutable slice or array as arr.reverse(); to reverse it in place.

2. Step 2: Check other options for errors

   arr = arr.reverse(); tries to assign the result of reverse() which returns (), so it's invalid. arr.reverse(&mut arr); passes &mut arr as argument, but reverse() takes no arguments. reverse(arr); calls a function reverse which is undefined.

3. Final Answer:

   arr.reverse(); -> Option B

4. Quick Check:

   Use method directly on mutable array [OK]

Hint: Use arr.reverse() without assignment or arguments [OK]

Common Mistakes:

• Assigning reverse() result to array
• Passing array as argument to reverse()
• Calling undefined reverse function

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

let mut arr = [1, 2, 3, 4, 5];
arr.reverse();
println!("{:?}", arr);

medium

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

B. [1, 2, 3, 4, 5]

C. [5, 4, 3, 2, 1]

D. Compilation error

Solution

1. Step 1: Understand reverse() effect on array

   The reverse() method reverses the array elements in place, so the order becomes last to first.

2. Step 2: Apply reverse to given array

   Original array is [1, 2, 3, 4, 5]. After reversal, it becomes [5, 4, 3, 2, 1].

3. Final Answer:

   [5, 4, 3, 2, 1] -> Option C

4. Quick Check:

   Reverse flips array order [OK]

Hint: Reverse flips array elements order [OK]

Common Mistakes:

• Expecting original order after reverse
• Thinking reverse sorts array
• Confusing output format

4. Identify the error in this Rust code that tries to reverse an array:

let arr = [10, 20, 30, 40];
arr.reverse();

medium

A. Cannot call reverse() on an immutable array

B. reverse() method does not exist for arrays

C. Missing semicolon after array declaration

D. reverse() requires an argument

Solution

1. Step 1: Check mutability of array

   The array arr is declared immutable by default with let. The reverse() method requires a mutable array.

2. Step 2: Understand method requirements

   To reverse in place, the array must be mutable, declared as let mut arr. Otherwise, calling reverse() causes a compile error.

3. Final Answer:

   Cannot call reverse() on an immutable array -> Option A

4. Quick Check:

   reverse() needs mutable array [OK]

Hint: Make array mutable with 'mut' before reversing [OK]

Common Mistakes:

• Forgetting to add 'mut' to array declaration
• Thinking reverse() needs arguments
• Assuming reverse() is not available for arrays

5. Given a vector vec = vec![1, 2, 3, 4, 5], which code snippet correctly reverses it and returns a new reversed vector without modifying the original?

hard

A. let rev_vec = vec.into_iter().reverse().collect();

B. vec.reverse(); let rev_vec = vec.clone();

C. let rev_vec = vec.reverse();

D. let rev_vec = vec.iter().rev().cloned().collect::();

Solution

1. Step 1: Understand vector reversal without mutation

   To reverse without changing original, use iterator rev() on iter(), clone elements, then collect into new vector.

2. Step 2: Analyze options

   let rev_vec = vec.iter().rev().cloned().collect::(); uses vec.iter().rev().cloned().collect() which creates a new reversed vector. vec.reverse(); let rev_vec = vec.clone(); reverses original vector in place, modifying it. let rev_vec = vec.reverse(); tries to assign reverse() result which is (), invalid. let rev_vec = vec.into_iter().reverse().collect(); uses into_iter() which consumes the original vector, so it doesn't leave the original unmodified.

3. Final Answer:

   let rev_vec = vec.iter().rev().cloned().collect::(); -> Option D

4. Quick Check:

   Use iter().rev().cloned().collect() for new reversed vector [OK]

Hint: Use iter().rev().cloned().collect() for reversed copy [OK]

Common Mistakes:

• Modifying original vector instead of copying
• Assigning reverse() result directly
• Using invalid reverse() on iterator