2019: day06: part 1

aoc2019/src/day06.rs

@@ -0,0 +1,77 @@
+use std::collections::HashMap;
+
+use aoc::err;
+use aoc::Result;
+
+const INPUT: &str = include_str!("../input/day06.txt");
+
+pub fn run() -> Result<()> {
+    println!("part 1: {}", part1(INPUT)?);
+
+    Ok(())
+}
+
+fn count_orbits(
+    key: &str,
+    orbits: &HashMap<String, String>,
+    cache: &mut HashMap<String, u64>,
+) -> u64 {
+    match cache.get(key) {
+        Some(val) => *val,
+        None => {
+            let val = match orbits.get(key) {
+                Some(parent) => count_orbits(parent, orbits, cache) + 1,
+                None => 0,
+            };
+            cache.insert(key.to_string(), val);
+            val
+        }
+    }
+}
+
+fn part1(input: &str) -> Result<u64> {
+    let orbits = input
+        .lines()
+        .map(|line| line.trim_end())
+        .map(|line| {
+            let paren = line
+                .find(')')
+                .ok_or_else(|| err!("couldn't find `)` in line: {}", line))?;
+            Ok((line[paren + 1..].to_string(), line[..paren].to_string()))
+        })
+        .collect::<Result<HashMap<String, String>>>()?;
+
+    let mut cache = HashMap::new();
+    Ok(orbits
+        .keys()
+        .map(|k| count_orbits(&k, &orbits, &mut cache))
+        .sum())
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    const PROVIDED1: &str = "COM)B
+B)C
+C)D
+D)E
+E)F
+B)G
+G)H
+D)I
+E)J
+J)K
+K)L
+";
+
+    #[test]
+    fn part1_provided() {
+        assert_eq!(part1(PROVIDED1).unwrap(), 42);
+    }
+
+    #[test]
+    fn part1_real() {
+        assert_eq!(part1(INPUT).unwrap(), 140608);
+    }
+}

aoc2019/src/lib.rs

@@ -3,3 +3,4 @@ pub mod day02;
 pub mod day03;
 pub mod day04;
 pub mod day05;
+pub mod day06;

aoc2019/src/main.rs

@@ -5,9 +5,17 @@ use aoc2019::day02;
 use aoc2019::day03;
 use aoc2019::day04;
 use aoc2019::day05;
+use aoc2019::day06;
 
 fn main() -> Result<()> {
-    let days: &[fn() -> Result<()>] = &[day01::run, day02::run, day03::run, day04::run, day05::run];
+    let days: &[fn() -> Result<()>] = &[
+        day01::run,
+        day02::run,
+        day03::run,
+        day04::run,
+        day05::run,
+        day06::run,
+    ];
 
     aoc::run(days)
 }