2021: day08: part 1

aoc2021/src/day08.rs

@@ -0,0 +1,68 @@
+use std::fmt::Write;
+
+use anyhow::{Context, Result};
+
+const INPUT: &str = include_str!("../input/day08.txt");
+
+pub fn run() -> Result<String> {
+    let mut res = String::with_capacity(128);
+
+    writeln!(res, "part 1: {}", part1(INPUT)?)?;
+
+    Ok(res)
+}
+
+fn part1(input: &str) -> Result<usize> {
+    let entries = input
+        .lines()
+        .map(TryInto::try_into)
+        .collect::<Result<Vec<Entry>>>()?;
+
+    Ok(entries.iter().map(Entry::count_easy_digits_in_output).sum())
+}
+
+struct Entry<'a> {
+    four_digits_output: Vec<&'a str>,
+}
+
+impl<'a> Entry<'a> {
+    fn count_easy_digits_in_output(&self) -> usize {
+        self.four_digits_output
+            .iter()
+            .filter(|digit| Self::is_easy_digit(digit))
+            .count()
+    }
+
+    fn is_easy_digit(digit: &str) -> bool {
+        matches!(digit.len(), 2 | 3 | 4 | 7)
+    }
+}
+
+impl<'a> TryFrom<&'a str> for Entry<'a> {
+    type Error = anyhow::Error;
+
+    fn try_from(s: &'a str) -> Result<Self, Self::Error> {
+        let (_, output) = s.split_once(" | ").context("couldn't split on ` | `")?;
+
+        Ok(Self {
+            four_digits_output: output.trim().split(' ').collect(),
+        })
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    const PROVIDED: &str = include_str!("../input/day08_provided.txt");
+
+    #[test]
+    fn part1_provided() {
+        assert_eq!(part1(PROVIDED).unwrap(), 26);
+    }
+
+    #[test]
+    fn part1_real() {
+        assert_eq!(part1(INPUT).unwrap(), 488);
+    }
+}

aoc2021/src/lib.rs

@@ -7,3 +7,4 @@ pub mod day04;
 pub mod day05;
 pub mod day06;
 pub mod day07;
+pub mod day08;

aoc2021/src/main.rs

@@ -9,6 +9,7 @@ use aoc2021::day04;
 use aoc2021::day05;
 use aoc2021::day06;
 use aoc2021::day07;
+use aoc2021::day08;
 
 fn main() -> Result<()> {
     let days: &[DayFunc] = &[
@@ -19,6 +20,7 @@ fn main() -> Result<()> {
         day05::run,
         day06::run,
         day07::run,
+        day08::run,
     ];
 
     aoc::run(days)