Rust Platform

🎯 In Python, you might check a palindrome like this:

cleaned = "".join(c.lower() for c in s if c.isalnum())
return cleaned == cleaned[::-1]

This exercise is about doing the same thing in Rust — but it's a great chance to practice composing iterator chains, combining the tools you've picked up in the previous exercises.

char methods you'll find useful

Rust's char type has built-in methods that mirror Python's str methods, but they work on individual characters:

'A'.is_alphanumeric()   // true  (like Python's str.isalnum())
'!'.is_alphanumeric()   // false
'A'.to_lowercase()      // an iterator yielding 'a'

One subtlety: char::to_lowercase() returns an iterator, not a single char. Why? Because some Unicode characters lowercase into multiple characters (e.g., German ß). This means you can't just .map() it into a single char — you'll need .flat_map() to flatten those inner iterators into one stream:

let letters: String = "Hello!"
    .chars()
    .flat_map(|c| c.to_lowercase())
    .collect();
// "hello!"

.flat_map() is like .map() followed by .flatten() — if your closure returns an iterator (or Option, or Vec), it unpacks the results into a single flat sequence. Python's equivalent is roughly a nested comprehension: [x for group in items for x in group].

The turbofish ::<Type>

Sometimes .collect() can't infer the target type from context. You can specify it inline with turbofish syntax:

let s = some_iterator.collect::<String>();

This is equivalent to let s: String = some_iterator.collect(); — just a different place to put the type annotation.