Day 1.

.gitignore

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+Cargo.lock
+target/

Cargo.toml

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+[package]
+name = "aoc"
+version = "0.1.0"
+authors = ["awick"]
+edition = "2018"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]
+clap = "^2.33.0"

inputs/day1

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src/main.rs

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+use clap::{App,Arg,SubCommand};
+
+fn is_number(s: String) -> Result<(), String> {
+    match u64::from_str_radix(&s, 10) {
+        Ok(_) => Ok(()),
+        Err(e) => Err(e.to_string()),
+    }
+}
+
+fn calculate_base_fuel(mass: u64) -> u64 {
+    let div3 = mass / 3;
+
+    if div3 >= 2 {
+        div3 - 2
+    } else {
+        0
+    }
+}
+
+fn calculate_fuel(mass: u64) -> u64 {
+    let mut res = calculate_base_fuel(mass);
+    let mut last_round = res;
+
+    loop {
+        let new_round = calculate_base_fuel(last_round);
+        if new_round == 0 {
+            return res;
+        } else {
+            res += new_round;
+            last_round = new_round;
+        }
+    }
+}
+
+fn main() {
+    let matches = App::new("My Advent of Code Thing")
+                      .version("1.0")
+                      .author("Adam Wick <awick@uhsure.com>")
+                      .about("Runs advent of code programs")
+                      .subcommand(SubCommand::with_name("fuel")
+                                    .about("runs the fuel computation from day1")
+                                    .arg(Arg::with_name("NUM")
+                                             .help("The mass of the ship")
+                                             .multiple(true)
+                                             .validator(is_number)))
+                      .get_matches();
+
+    if let Some(problem1) = matches.subcommand_matches("fuel") {
+        let mut total = 0;
+
+        match problem1.values_of("NUM") {
+            None =>
+                println!("ERROR: No values to compute fuel for!"),
+            Some(masses) => {
+                for mass_str in masses {
+                    let mass = u64::from_str_radix(&mass_str, 10).unwrap();
+                    let fuel = calculate_fuel(mass);
+                    println!("Mass {}: {} fuel", mass, fuel);
+                    total += fuel;
+                }
+
+                println!("TOTAL FUEL: {}", total);
+                std::process::exit(0);
+            }
+        }
+    }
+
+    println!("Failed to run a reasonable command.");
+}