Day2.rs

use std::collections::HashSet;

impl Solution {  
    pub fn is_happy(n: i32) -> bool {
        if n == 1 { return true; }
        let mut cur: i32 = n;
        let mut seen: HashSet<i32> = HashSet::new();
        
        loop {
            // Split into array, fold into values and reset as cur.
            let result = cur.to_string()
               .chars().map(|d| 
                   d.to_digit(10).unwrap() as i32
                )
                .fold(0, |acc, x| acc + x.pow(2));
            if result == 1 {
                return true;
            }
            if !seen.insert(result) {
                return false;
            }
            cur = result;
        }
        return false;
    } 
}