Exercise 2: Sum of Squares

Difficulty: Beginner Concepts: Vec basics, iteration, fold, closures

Problem Statement

Write a function sum_of_squares that takes a slice of integers and returns the sum of their squares.

For example:

• [1, 2, 3] → 1² + 2² + 3² = 1 + 4 + 9 = 14
• [2, 4] → 2² + 4² = 4 + 16 = 20

Learning Goals

• Work with slices (&[T])
• Iterate over collections
• Use fold for accumulation
• Practice with closures
• Understand iterator methods

Examples

#![allow(unused)]
fn main() {
assert_eq!(sum_of_squares(&[1, 2, 3]), 14);
assert_eq!(sum_of_squares(&[2, 4]), 20);
assert_eq!(sum_of_squares(&[]), 0);
}

Starter Code

#![allow(unused)]
fn main() {
pub fn sum_of_squares(nums: &[i32]) -> i32 {
    // TODO: implement this function
    todo!()
}

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

    #[test]
    fn test_basic() {
        assert_eq!(sum_of_squares(&[1, 2, 3]), 14);
    }

    #[test]
    fn test_two_elements() {
        assert_eq!(sum_of_squares(&[2, 4]), 20);
    }

    #[test]
    fn test_empty() {
        assert_eq!(sum_of_squares(&[]), 0);
    }

    #[test]
    fn test_single() {
        assert_eq!(sum_of_squares(&[5]), 25);
    }

    #[test]
    fn test_negative() {
        assert_eq!(sum_of_squares(&[-3, 4]), 25);
    }

    #[test]
    fn test_zeros() {
        assert_eq!(sum_of_squares(&[0, 0, 0]), 0);
    }
}
}

Follow-up Challenges

1. Make it generic over any numeric type: sum_of_squares<T>(nums: &[T]) -> T
2. Implement sum_of_cubes using the same pattern
3. Create a generic sum_of_powers(nums: &[i32], power: u32) -> i32
4. Use par_iter() from rayon for parallel computation (research exercise)

Key Takeaways

• &[T] is a slice - a view into a sequence of elements
• iter() creates an iterator over references to elements
• map() transforms each element
• sum() is a convenient method for numeric iterators
• fold() is the general accumulation pattern
• Closures |x| ... are anonymous functions
• Pattern |&x| destructures references in closure parameters

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