(6 kyu) Square Digits Sequence.rs

use std::collections::HashSet;

// #1
fn square_digits_sequence(a0: u32) -> usize {
    let mut nums: HashSet<u32> = HashSet::new();
    let mut x = a0;
    while !nums.contains(&x) {
        nums.insert(x);
        let digits: String = x.to_string();
        x = digits.chars().fold(0, |mut sum, d| {
            let n = d.to_digit(10).unwrap();
            sum += n * n;
            sum
        });
    }
    nums.len() + 1
}

// #2
fn square_digits_sequence(mut n: u32) -> usize {
    let mut seen = HashSet::new();
    while !seen.contains(&n) {
        seen.insert(n);
        n = n.to_string().chars().map(|c| c.to_digit(10).unwrap().pow(2)).sum();
    }
    seen.len() + 1   
}