Implement LeetCode (or similar) exercises in Rustings

[sergiosat92]

It would be great to add LeetCode-style exercises (or from other competitive programming platforms) into Rustlings so learners can practice Rust by solving real-world algorithmic and data structure problems.

Proposal:

• Select a curated list of beginner, intermediate, and advanced problems from LeetCode or other platforms.
• Implement them in the style of Rustlings exercises, with test-driven learning (#[test] failures guiding the user).
• Keep problems self-contained to avoid licensing issues (rewording original problem statements if necessary). The goal is to take it as a strong reference.

Example exercise:

// TODO: Implement a function that checks if a string is a palindrome
fn is_palindrome(s: &str) -> bool {
    unimplemented!()
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn test_palindrome() {
        assert!(is_palindrome("racecar"));
        assert!(!is_palindrome("rust"));
    }
}

[irfanghat]

@sergiosat92 that would be great. I think they wanted to focus mostly on learning/getting familiar with the syntax so anyone could dive in if they wanted to familiarize themselves with what rust has to offer in terms of syntax.