Completed day 6 part 1

day6/Cargo.lock

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+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+[[package]]
+name = "day6"
+version = "0.1.0"
+

day6/Cargo.toml

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+[package]
+name = "day6"
+version = "0.1.0"
+authors = ["Tyler Hallada <tyler@hallada.net>"]
+edition = "2018"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]

day6/input/test.txt

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+COM)B
+B)C
+C)D
+D)E
+E)F
+B)G
+G)H
+D)I
+E)J
+J)K
+K)L

day6/src/main.rs

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+use std::collections::HashMap;
+use std::error::Error;
+use std::fs::File;
+use std::io::{prelude::*, BufReader};
+use std::result;
+
+const INPUT: &str = "input/input.txt";
+
+type Result<T> = result::Result<T, Box<dyn Error>>;
+
+fn read_orbit_map(filename: &str) -> Result<HashMap<String, Option<String>>> {
+    let file = File::open(filename)?;
+    let reader = BufReader::new(file);
+    let mut objects: HashMap<String, Option<String>> = HashMap::new();
+
+    for line in reader.lines() {
+        let line = line?;
+        let mut parts = line.split(")");
+        let mass_name = parts
+            .next()
+            .expect("Invalid line, no mass part.")
+            .to_string();
+        let orbiter_name = parts
+            .next()
+            .expect("Invalid line, no orbiter part.")
+            .to_string();
+
+        objects.entry(mass_name.clone()).or_insert(None);
+        objects.insert(orbiter_name.clone(), Some(mass_name));
+    }
+
+    Ok(objects)
+}
+
+fn get_orbit_count(orbit_map: &HashMap<String, Option<String>>, orbiter: String) -> u32 {
+    match orbit_map.get(&orbiter) {
+        None => panic!("Incomplete orbit map"),
+        Some(mass) => match mass {
+            None => return 0,
+            Some(mass) => return 1 + get_orbit_count(orbit_map, mass.to_string()),
+        },
+    }
+}
+
+fn get_orbit_count_checksum(orbit_map: &HashMap<String, Option<String>>) -> u32 {
+    let mut checksum = 0;
+
+    for orbiter in orbit_map.keys() {
+        checksum += get_orbit_count(&orbit_map, orbiter.to_string());
+    }
+
+    checksum
+}
+
+fn solve_part1() -> Result<u32> {
+    let orbit_map = read_orbit_map(INPUT)?;
+    Ok(get_orbit_count_checksum(&orbit_map))
+}
+
+fn solve_part2() -> Result<i32> {
+    Ok(0)
+}
+
+fn main() -> Result<()> {
+    println!("Part 1: {}", solve_part1()?);
+    println!("Part 2: {}", solve_part2()?);
+
+    Ok(())
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    const TEST_INPUT: &str = "input/test.txt";
+
+    #[test]
+    fn reads_orbit_map() {
+        assert_eq!(
+            read_orbit_map(TEST_INPUT).unwrap(),
+            [
+                ("COM".to_string(), None),
+                ("B".to_string(), Some("COM".to_string())),
+                ("C".to_string(), Some("B".to_string())),
+                ("D".to_string(), Some("C".to_string())),
+                ("E".to_string(), Some("D".to_string())),
+                ("F".to_string(), Some("E".to_string())),
+                ("G".to_string(), Some("B".to_string())),
+                ("H".to_string(), Some("G".to_string())),
+                ("I".to_string(), Some("D".to_string())),
+                ("J".to_string(), Some("E".to_string())),
+                ("K".to_string(), Some("J".to_string())),
+                ("L".to_string(), Some("K".to_string())),
+            ]
+            .iter()
+            .cloned()
+            .collect()
+        );
+    }
+
+    #[test]
+    fn gets_orbit_count_checksum() {
+        let orbit_map = read_orbit_map(TEST_INPUT).unwrap();
+        assert_eq!(get_orbit_count_checksum(&orbit_map), 42)
+    }
+}