2020: day10: part 1

aoc2020/src/day10.rs

@@ -0,0 +1,65 @@
+use std::fmt::Write;
+
+use aoc::err;
+
+const INPUT: &str = include_str!("../input/day10.txt");
+
+pub fn run() -> aoc::Result<String> {
+    let mut res = String::with_capacity(128);
+
+    writeln!(res, "part 1: {}", part1(INPUT)?)?;
+
+    Ok(res)
+}
+
+fn part1(input: &str) -> aoc::Result<usize> {
+    let mut jolts = input
+        .lines()
+        .map(|line| {
+            line.parse()
+                .map_err(|e| err!("couldn't parse joltage: {}", e))
+        })
+        .collect::<aoc::Result<Vec<u64>>>()?;
+
+    if jolts.is_empty() {
+        return Err(err!("input was empty!"));
+    }
+
+    // charging outlet can be added
+    jolts.insert(0, 0);
+
+    jolts.sort_unstable();
+
+    // device is rated for max adapter + 3 jolts
+    let max_adapter = jolts[jolts.len() - 1];
+    let device_rating = max_adapter + 3;
+    jolts.push(device_rating);
+
+    let mut differences: [usize; 4] = [0; 4];
+
+    for (prev, next) in jolts.iter().zip(jolts.iter().skip(1)) {
+        let difference = (next - prev) as usize;
+        differences[difference] += 1;
+    }
+
+    Ok(differences[1] * differences[3])
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    const PROVIDED1: &str = include_str!("../input/day10_provided1.txt");
+    const PROVIDED2: &str = include_str!("../input/day10_provided2.txt");
+
+    #[test]
+    fn part1_provided() {
+        assert_eq!(part1(PROVIDED1).unwrap(), 7 * 5);
+        assert_eq!(part1(PROVIDED2).unwrap(), 22 * 10);
+    }
+
+    #[test]
+    fn part1_real() {
+        assert_eq!(part1(INPUT).unwrap(), 2112);
+    }
+}

aoc2020/src/lib.rs

@@ -7,3 +7,4 @@ pub mod day06;
 pub mod day07;
 pub mod day08;
 pub mod day09;
+pub mod day10;

aoc2020/src/main.rs

@@ -10,6 +10,7 @@ use aoc2020::day06;
 use aoc2020::day07;
 use aoc2020::day08;
 use aoc2020::day09;
+use aoc2020::day10;
 
 fn main() -> Result<()> {
     let days: &[DayFunc] = &[
@@ -22,6 +23,7 @@ fn main() -> Result<()> {
         day07::run,
         day08::run,
         day09::run,
+        day10::run,
     ];
 
     aoc::run(days)