String Reversal Approaches in DSA Rust - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to reverse a string using the built-in method.

DSA Rust

let original = String::from("hello");
let reversed: String = original.chars().rev().[1]();
println!("{}", reversed);

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

Ato_string()

Bclone()

Cunwrap()

Dcollect()

Attempts:

3 left

💡 Hint

Common Mistakes

Using to_string() instead of collect() after rev()

Trying to unwrap() the iterator

Using clone() which does not reverse

The rev() method returns an iterator, so we use collect() to gather the characters back into a String.

2fill in blank

medium

Complete the code to reverse a string by converting it to a vector of chars and reversing in place.

DSA Rust

let mut chars: Vec<char> = original.chars().collect();
chars.[1]();
let reversed: String = chars.into_iter().collect();
println!("{}", reversed);

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Arev

Breverse

Csort

Dsort_unstable

Attempts:

3 left

💡 Hint

Common Mistakes

Using rev() on Vec which is invalid

Using sort() which sorts instead of reversing

Using sort_unstable() which also sorts

The reverse() method reverses the vector in place. rev() is an iterator adapter and cannot be called on Vec directly.

3fill in blank

hard

Fix the error in the code to reverse a string by swapping characters in place.

DSA Rust

let mut chars: Vec<char> = original.chars().collect();
let len = chars.len();
for i in 0..len / 2 {
    chars.swap(i, len - 1 - [1]);
}
let reversed: String = chars.into_iter().collect();
println!("{}", reversed);

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Ai

B0

Clen

D1

Attempts:

3 left

💡 Hint

Common Mistakes

Using len or 0 instead of i causes index errors

Using 1 shifts the index incorrectly

We swap the character at index i with the character at index len - 1 - i to reverse the vector in place.

4fill in blank

hard

Fill in the blank to create a reversed string using iterator methods and filter vowels.

DSA Rust

let reversed_vowels: String = original.chars().rev().filter(|c| "aeiouAEIOU".[1](c)).collect();

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Ais_ascii

Bstarts_with

Ccontains

Dends_with

Attempts:

3 left

💡 Hint

Common Mistakes

Using starts_with or ends_with which check prefixes or suffixes

Using is_ascii which checks character encoding

The contains() method checks if the vowels string contains the character c, filtering only vowels.

5fill in blank

hard

Fill all three blanks to create a reversed string with uppercase letters only.

DSA Rust

let reversed_uppercase: String = original.chars().rev().filter(|c| c.is_alphabetic() && c.[1]()).map(|c| c.[2]()).flatten().collect::<String>().[3]();

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Ais_lowercase

Bto_uppercase

Cto_string

Dto_lowercase

Attempts:

3 left

💡 Hint

Common Mistakes

Using to_lowercase instead of to_uppercase

Not converting the iterator to String properly

Filtering with is_uppercase instead of is_lowercase

We filter lowercase alphabetic characters, convert them to uppercase, collect into a String, then convert the iterator to String with to_string().

Practice

1. What does the chars().rev().collect() method chain do when applied to a Rust string?

easy

A. It reverses the characters of the string and collects them into a new string.

B. It sorts the characters of the string in ascending order.

C. It removes all whitespace characters from the string.

D. It converts the string to uppercase.

Solution

1. Step 1: Understand chars() method

   The chars() method converts the string into an iterator over its characters.

2. Step 2: Apply rev() and collect()

   The rev() method reverses the iterator, and collect() gathers the reversed characters into a new string.

3. Final Answer:

   It reverses the characters of the string and collects them into a new string. -> Option A

4. Quick Check:

   chars().rev().collect() reverses string [OK]

Hint: Remember: chars() + rev() + collect() reverses a string [OK]

Common Mistakes:

• Thinking it sorts characters instead of reversing
• Confusing rev() with removing characters
• Assuming it changes case of letters

2. Which of the following Rust code snippets correctly reverses a string s?

easy

A. let reversed: String = s.reverse();

B. let reversed: String = s.chars().rev().collect();

C. let reversed: String = s.collect().rev().chars();

D. let reversed: String = s.chars().collect().rev();

Solution

1. Step 1: Check method availability

   Rust strings do not have a reverse() method, so let reversed: String = s.reverse(); is invalid.

2. Step 2: Analyze method chaining

   let reversed: String = s.chars().rev().collect(); uses chars() to get characters, rev() to reverse, and collect() to form a new string, which is correct.

3. Final Answer:

   let reversed: String = s.chars().rev().collect(); -> Option B

4. Quick Check:

   Correct syntax for string reversal is let reversed: String = s.chars().rev().collect(); [OK]

Hint: Use chars().rev().collect() to reverse strings in Rust [OK]

Common Mistakes:

• Using non-existent reverse() method on String
• Wrong order of method calls
• Trying to reverse after collecting into String

3. What is the output of the following Rust code?

let s = String::from("rust");
let reversed: String = s.chars().rev().collect();
println!("{}", reversed);

medium

A. Error: cannot reverse string

B. rust

C. tsur

D. tusr

Solution

1. Step 1: Understand input string

   The string "rust" has characters 'r', 'u', 's', 't'.

2. Step 2: Reverse characters and collect

   Using chars().rev().collect() reverses the characters to 't', 's', 'u', 'r' and collects into a new string.

3. Final Answer:

   tsur -> Option C

4. Quick Check:

   Reversed "rust" = "tsur" [OK]

Hint: Trace chars().rev().collect() to get reversed string output [OK]

Common Mistakes:

• Expecting original string output
• Mixing character order incorrectly
• Assuming runtime error on reversal

4. Identify the error in this Rust code that attempts to reverse a string:

let s = String::from("hello");
let reversed = s.reverse();
println!("{}", reversed);

medium

A. reverse() returns a vector, not a string

B. Missing semicolon after println! macro

C. Cannot print reversed string directly

D. String type has no method named reverse()

Solution

1. Step 1: Check method existence on String

   Rust's String type does not have a reverse() method, so calling it causes a compile error.

2. Step 2: Confirm other syntax correctness

   The semicolon after println! is present, and printing a string is valid, so no errors there.

3. Final Answer:

   String type has no method named reverse() -> Option D

4. Quick Check:

   reverse() method does not exist on String [OK]

Hint: Remember: String has no reverse() method in Rust [OK]

Common Mistakes:

• Assuming reverse() exists on String
• Thinking reverse() returns vector automatically
• Ignoring compiler error messages

5. You want to reverse a string but keep all Unicode grapheme clusters intact (like emojis or accented letters). Which Rust crate and approach is best suited for this?

hard

A. Use the unicode-segmentation crate to split by graphemes, then reverse and collect.

B. Use chars().rev().collect() directly on the string.

C. Convert string to bytes, reverse bytes, then convert back to string.

D. Use split_whitespace() and reverse the words.

Solution

1. Step 1: Understand Unicode grapheme clusters

   Some characters like emojis or accented letters are multiple Unicode code points but one visible character (grapheme cluster).

2. Step 2: Use appropriate crate and method

   The unicode-segmentation crate provides graphemes() method to split string by grapheme clusters, which can then be reversed safely.

3. Final Answer:

   Use the unicode-segmentation crate to split by graphemes, then reverse and collect. -> Option A

4. Quick Check:

   unicode-segmentation crate handles grapheme reversal correctly [OK]

Hint: Use unicode-segmentation crate for correct Unicode string reversal [OK]

Common Mistakes:

• Reversing by chars() breaks multi-codepoint characters
• Reversing bytes corrupts UTF-8 encoding
• Reversing words instead of characters