Day 1

2 files changed, 107 insertions, 1 deletions

diff --git a/src/bin/day_1.rs b/src/bin/day_1.rs
new file mode 100644
index 0000000..7c8f104
--- /dev/null
+++ b/src/bin/day_1.rs
@@ -0,0 +1,97 @@
+use std::io;
+use std::io::prelude::*;
+use std::iter;
+use std::iter::Sum;
+use std::num::ParseIntError;
+use std::ops::Add;
+use std::str::FromStr;
+
+fn main() {
+    let stdin = io::stdin();
+
+    let input = stdin
+        .lock()
+        .lines()
+        .map(|l| l.unwrap().parse::<Module>().unwrap());
+
+    dbg!(fuel_required(input));
+}
+
+// TODO: If this were a nice CLI program, it would probably have a switch to choose between these two rather than doing both?
+fn fuel_required(it: impl Iterator<Item = Module>) -> (Fuel, Fuel) {
+    it.map(|m| {
+        (
+            m.fuel_excluding_fuel_weight(),
+            m.fuel_including_fuel_weight(),
+        )
+    })
+    .fold((Fuel(0), Fuel(0)), |(sum_x, sum_y), (x, y)| {
+        (sum_x + x, sum_y + y)
+    })
+}
+
+struct Module {
+    weight: Weight,
+}
+
+impl FromStr for Module {
+    type Err = ParseIntError;
+
+    fn from_str(s: &str) -> Result<Self, Self::Err> {
+        Ok(Module {
+            weight: Weight(s.parse()?),
+        })
+    }
+}
+
+impl Module {
+    fn fuel_excluding_fuel_weight(&self) -> Fuel {
+        self.weight.required_fuel()
+    }
+
+    fn fuel_including_fuel_weight(&self) -> Fuel {
+        iter::successors(Some(self.weight.required_fuel()), |fuel| {
+            if fuel.weight().is_zero() {
+                None
+            } else {
+                Some(fuel.weight().required_fuel())
+            }
+        })
+        .sum()
+    }
+}
+
+struct Weight(u32);
+
+impl Weight {
+    fn is_zero(&self) -> bool {
+        self.0 == 0
+    }
+
+    fn required_fuel(&self) -> Fuel {
+        Fuel((self.0 / 3).saturating_sub(2))
+    }
+}
+
+#[derive(Debug)]
+struct Fuel(u32);
+
+impl Fuel {
+    fn weight(&self) -> Weight {
+        Weight(self.0)
+    }
+}
+
+impl Add for Fuel {
+    type Output = Self;
+
+    fn add(self, other: Self) -> Self {
+        Fuel(self.0 + other.0)
+    }
+}
+
+impl Sum for Fuel {
+    fn sum<I: Iterator<Item = Self>>(iter: I) -> Self {
+        iter.fold(Fuel(0), Add::add)
+    }
+}
diff --git a/src/main.rs b/src/main.rs
index e7a11a9..0c24a73 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -1,3 +1,12 @@
+use std::io;
+use std::io::prelude::*;
+
 fn main() {
-    println!("Hello, world!");
+    let stdin = io::stdin();
+    let answer = string_length_sum(stdin.lock().lines().map(|l| l.unwrap()));
+    dbg!(answer);
+}
+
+fn string_length_sum(it: impl Iterator<Item = String>) -> usize {
+    it.map(|l| l.len()).sum()
 }