Palindrome Detection in DSA Rust - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to check if a string is the same forwards and backwards.

DSA Rust

fn is_palindrome(s: &str) -> bool {
    s == s.chars().rev().[1]::<String>()
}

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

Ato_vec

Bto_string

Ccollect

Dclone

Attempts:

3 left

💡 Hint

Common Mistakes

Using collect() without specifying the type causes errors.

Using to_vec() returns a vector, not a String.

The reversed characters are collected into a new String using collect::() to compare with the original.

2fill in blank

medium

Complete the code to ignore case when checking palindrome.

DSA Rust

fn is_palindrome_ignore_case(s: &str) -> bool {
    let lower = s.to_lowercase();
    lower == lower.chars().rev().[1]::<String>()
}

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

Acollect

Bclone

Cto_string

Dto_vec

Attempts:

3 left

💡 Hint

Common Mistakes

Using to_vec() returns a vector, not a String.

Forgetting to convert to lowercase before comparison.

After reversing, we convert the characters back to a String with collect::() to compare ignoring case.

3fill in blank

hard

Fix the error in the code to correctly check palindrome ignoring spaces.

DSA Rust

fn is_palindrome_ignore_spaces(s: &str) -> bool {
    let filtered: String = s.chars().filter(|c| !c.is_whitespace()).collect();
    filtered == filtered.chars().rev().[1]::<String>()
}

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

Aclone

Bcollect

Cto_string

Dto_vec

Attempts:

3 left

💡 Hint

Common Mistakes

Using to_vec() returns a vector, not a String.

Not filtering out whitespace before comparison.

We must convert the reversed characters into a String using collect::() for correct comparison.

4fill in blank

hard

Fill both blanks to create a palindrome check ignoring punctuation and case.

DSA Rust

fn is_palindrome_clean(s: &str) -> bool {
    let filtered: String = s.chars().filter(|c| c.is_alphanumeric()).map(|c| c.to_lowercase().[1]().unwrap()).collect();
    filtered == filtered.chars().rev().[2]::<String>()
}

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

Anext

Bto_string

Ccollect

Dclone

Attempts:

3 left

💡 Hint

Common Mistakes

Using to_string() directly on to_lowercase() without next() causes errors.

Not collecting reversed chars into a String.

Each character's lowercase iterator returns an iterator, so next() gets the char. Then reversed chars are collected into a String with collect::().

5fill in blank

hard

Fill both blanks to create a palindrome check ignoring case, spaces, and punctuation.

DSA Rust

fn is_palindrome_full(s: &str) -> bool {
    let filtered: String = s.chars()
        .filter(|c| c.is_alphanumeric())
        .map(|c| c.to_lowercase().[1]().unwrap())
        .collect();
    filtered == filtered.chars().rev().[2]::<String>()
}

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

Anext

Bcollect

Cclone

Dto_vec

Attempts:

3 left

💡 Hint

Common Mistakes

Using to_string() directly on to_lowercase() without next() causes errors.

Not collecting reversed chars into a String.

Use next() to get the lowercase char, then collect reversed chars into a String with collect::().

Practice

1. What does a palindrome string mean in simple terms?

easy

A. It has all unique characters

B. It contains only vowels

C. It is always an even length string

D. It reads the same forwards and backwards

Solution

1. Step 1: Understand palindrome definition

   A palindrome is a word or phrase that reads the same from left to right and right to left.

2. Step 2: Check options against definition

   Only It reads the same forwards and backwards matches this meaning exactly.

3. Final Answer:

   It reads the same forwards and backwards -> Option D

4. Quick Check:

   Palindrome = Same forwards and backwards [OK]

Hint: Palindrome means mirror reading same both ways [OK]

Common Mistakes:

• Confusing palindrome with unique characters
• Thinking palindrome must be even length
• Assuming palindrome only has vowels

2. Which Rust code snippet correctly checks if a string s is a palindrome?

easy

A. s.reverse() == s

B. s.chars().eq(s.chars().rev())

C. s == s.reverse()

D. s.chars().all(|c| c == s.chars().next().unwrap())

Solution

1. Step 1: Understand Rust string palindrome check

   To check palindrome, compare characters iterator with its reverse iterator.

2. Step 2: Analyze options

   s.chars().eq(s.chars().rev()) uses chars().eq(chars().rev()) which correctly compares forward and backward characters. Options A and C use invalid methods or wrong comparisons. s.chars().all(|c| c == s.chars().next().unwrap()) checks if all characters are same, not palindrome.

3. Final Answer:

   s.chars().eq(s.chars().rev()) -> Option B

4. Quick Check:

   Compare chars iterator with reversed iterator [OK]

Hint: Use chars().eq(chars().rev()) to check palindrome [OK]

Common Mistakes:

• Using reverse() method on &str which does not exist
• Comparing string with reversed string incorrectly
• Checking all chars equal instead of palindrome

3. What is the output of this Rust code?

let s = "racecar";
let result = s.chars().eq(s.chars().rev());
println!("{}", result);

medium

A. true

B. Runtime panic

C. Compilation error

D. false

Solution

1. Step 1: Analyze the string and palindrome check

   The string "racecar" reads the same forwards and backwards, so it is a palindrome.

2. Step 2: Understand the code output

   The code compares characters forward and backward and returns true for palindrome strings. So, it prints true.

3. Final Answer:

   true -> Option A

4. Quick Check:

   "racecar" palindrome check = true [OK]

Hint: Check if string equals its reverse chars [OK]

Common Mistakes:

• Assuming palindrome check returns false for odd length
• Thinking code causes compile or runtime error
• Confusing output with string itself

4. Identify the error in this Rust palindrome check code:

fn is_palindrome(s: &str) -> bool {
    s == s.chars().rev().collect::<String>()
}

medium

A. Cannot compare &str with String directly

B. Missing semicolon after collect

C. chars().rev() does not exist

D. Function return type should be String

Solution

1. Step 1: Understand types in comparison

   The left side is &str, right side is String from collect(). Direct comparison between &str and String is not allowed.

2. Step 2: Fix type mismatch

   Convert left side to String or right side to &str for comparison. For example, use s.to_string() == s.chars().rev().collect::<String>().

3. Final Answer:

   Cannot compare &str with String directly -> Option A

4. Quick Check:

   Type mismatch in comparison causes error [OK]

Hint: Compare same types: &str vs &str or String vs String [OK]

Common Mistakes:

• Ignoring type mismatch error
• Assuming collect needs semicolon inside expression
• Thinking chars().rev() is invalid method

5. You want to detect palindromes ignoring case and spaces in Rust. Which code snippet correctly implements this?

hard

A. let is_pal = s.chars().all(|c| c.is_alphanumeric());

B. let lower = s.to_lowercase();
let is_pal = lower == lower.reverse();

C. let filtered: String = s.chars().filter(|c| !c.is_whitespace()).collect();
let lower = filtered.to_lowercase();
let is_pal = lower.chars().eq(lower.chars().rev());

D. let filtered: String = s.chars().filter(|c| c.is_whitespace()).collect();
let is_pal = filtered == filtered.chars().rev().collect::<String>();

Solution

1. Step 1: Remove spaces and convert to lowercase

   let filtered: String = s.chars().filter(|c| !c.is_whitespace()).collect(); let lower = filtered.to_lowercase(); let is_pal = lower.chars().eq(lower.chars().rev()); filters out whitespace, collects characters, then converts to lowercase string.

2. Step 2: Check palindrome on cleaned string

   It compares characters forward and backward correctly on the cleaned lowercase string.

3. Final Answer:

   let filtered: String = s.chars().filter(|c| !c.is_whitespace()).collect(); let lower = filtered.to_lowercase(); let is_pal = lower.chars().eq(lower.chars().rev()); -> Option C

4. Quick Check:

   Filter spaces + lowercase + compare reversed chars [OK]

Hint: Clean string first: remove spaces, lowercase, then check palindrome [OK]

Common Mistakes:

• Using reverse() method which does not exist
• Filtering only whitespace but not converting case
• Checking all chars alphanumeric instead of palindrome