1 files changed, 93 insertions, 0 deletions
diff --git a/2019/src/bin/day_1.rs b/2019/src/bin/day_1.rs
new file mode 100644
index 0000000..572d287
--- /dev/null
+++ b/2019/src/bin/day_1.rs
@@ -0,0 +1,93 @@
+use derive_more;
+use std::io;
+use std::io::prelude::*;
+use std::iter;
+use std::process;
+
+use structopt::StructOpt;
+
+#[derive(Debug, StructOpt)]
+#[structopt(name = "Day 1: The Tyranny of the Rocket Equation")]
+/// Calculates the fuel needed for your rocket to save Santa.
+///
+/// The weight of each module is read from stdin, one module weight
+/// per line. See https://adventofcode.com/2019/day/1 for details.
+struct Opt {
+    /// Includes the weight of fuel
+    #[structopt(short = "i", long = "include-fuel-weight")]
+    include_fuel_weight: bool,
+}
+
+fn main() {
+    let stdin = io::stdin();
+    let opt = Opt::from_args();
+
+    let input = stdin.lock().lines().map(|l| match l {
+        Ok(s) => match s.parse::<Module>() {
+            Ok(module) => module,
+            Err(e) => {
+                eprintln!("Invalid input \"{}\": {}", s, e);
+                process::exit(1);
+            }
+        },
+        Err(e) => {
+            eprintln!("Error reading input: {}", e);
+            process::exit(1);
+        }
+    });
+
+    println!("{}", fuel_required(input, opt.include_fuel_weight))
+}
+
+fn fuel_required(it: impl Iterator<Item = Module>, include_fuel_weight: bool) -> Fuel {
+    it.map(if include_fuel_weight {
+        Module::fuel_including_fuel_weight
+    } else {
+        Module::fuel_excluding_fuel_weight
+    })
+    .sum()
+}
+
+#[derive(Debug, derive_more::FromStr, Clone, Copy)]
+struct Module {
+    weight: Weight,
+}
+
+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.is_zero() {
+                None
+            } else {
+                Some(fuel.weight().required_fuel())
+            }
+        })
+        .sum()
+    }
+}
+
+#[derive(Debug, derive_more::FromStr, Clone, Copy)]
+struct Weight(u32);
+
+impl Weight {
+    fn required_fuel(self) -> Fuel {
+        Fuel((self.0 / 3).saturating_sub(2))
+    }
+}
+
+#[derive(Debug, derive_more::Add, derive_more::Sum, Clone, Copy, derive_more::Display)]
+struct Fuel(u32);
+
+impl Fuel {
+    fn weight(self) -> Weight {
+        Weight(self.0)
+    }
+
+    fn is_zero(self) -> bool {
+        self.0 == 0
+    }
+}