2019: day01: part 2

aoc2019/src/day01.rs

@@ -4,12 +4,16 @@ const INPUT: &str = include_str!("../input/day01.txt");
 
 pub fn run() -> Result<()> {
     println!("part 1: {}", part1(INPUT)?);
+    println!("part 2: {}", part2(INPUT)?);
 
     Ok(())
 }
 
 fn fuel_needed(module_weight: u64) -> u64 {
-    (module_weight / 3) - 2
+    match (module_weight / 3).checked_sub(2) {
+        Some(f) => f,
+        None => 0,
+    }
 }
 
 fn part1(input: &str) -> Result<u64> {
@@ -23,6 +27,29 @@ fn part1(input: &str) -> Result<u64> {
         .sum()
 }
 
+fn cumulated_fuel_needed(module_weight: u64) -> u64 {
+    let mut total_fuel = fuel_needed(module_weight);
+    let mut additional_fuel = fuel_needed(total_fuel);
+
+    while additional_fuel != 0 {
+        total_fuel += additional_fuel;
+        additional_fuel = fuel_needed(additional_fuel);
+    }
+
+    total_fuel
+}
+
+fn part2(input: &str) -> Result<u64> {
+    input
+        .lines()
+        .map(|line| line.parse::<u64>())
+        .map(|w| match w {
+            Ok(w) => Ok(cumulated_fuel_needed(w)),
+            Err(e) => Err(Box::from(e)),
+        })
+        .sum()
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;
@@ -39,4 +66,16 @@ mod tests {
     fn part1_real() {
         assert_eq!(part1(INPUT).unwrap(), 3268951);
     }
+
+    #[test]
+    fn part2_provided() {
+        assert_eq!(cumulated_fuel_needed(14), 2);
+        assert_eq!(cumulated_fuel_needed(1969), 966);
+        assert_eq!(cumulated_fuel_needed(100756), 50346);
+    }
+
+    #[test]
+    fn part2_real() {
+        assert_eq!(part2(INPUT).unwrap(), 4900568);
+    }
 }