Add Rust solutions for days 1-3

Signed-off-by: Alek Ratzloff <alekr@jsausa.com>

day01/Day01.rs

@@ -0,0 +1,56 @@
+use std::io::{self, Read};
+
+type Result<T> = std::result::Result<T, Box<dyn std::error::Error>>;
+
+fn get_input_string() -> io::Result<String> {
+    let mut buffer = String::new();
+    io::stdin().read_to_string(&mut buffer)?;
+    Ok(buffer)
+}
+
+fn main() -> Result<()> {
+    let mass_list: Vec<_> = get_input_string()?
+        .split("\n")
+        .filter(|n| !n.is_empty())
+        .map(|n| n.parse::<u64>().unwrap())
+        .collect();
+    part1(&mass_list);
+    part2(&mass_list);
+    Ok(())
+}
+
+fn part1(mass_list: &Vec<u64>) {
+    let total: u64 = mass_list.iter()
+        .copied()
+        .map(fuel_req)
+        .sum();
+
+    println!("Part 1: {}", total);
+}
+
+fn fuel_req(mass: u64) -> u64 {
+    let frac = mass / 3;
+    if frac <= 2 {
+        0
+    } else {
+        frac - 2
+    }
+}
+
+fn part2(mass_list: &Vec<u64>) {
+    let total: u64 = mass_list.iter()
+        .copied()
+        .map(full_fuel_req)
+        .sum();
+    
+    println!("Part 2: {}", total);
+}
+
+fn full_fuel_req(mass: u64) -> u64 {
+    let req = fuel_req(mass);
+    if req == 0 {
+        0
+    } else {
+        req + full_fuel_req(req)
+    }
+}