Complete day 5

day05/src/main.rs

@@ -0,0 +1,119 @@
+use anyhow::{anyhow, Error, Result};
+
+use std::fs::File;
+use std::io::prelude::*;
+use std::io::BufReader;
+use std::str::FromStr;
+
+const INPUT: &str = "input/input.txt";
+
+#[derive(Debug, PartialEq)]
+struct Seat {
+    row: u32,
+    col: u32,
+}
+
+impl Seat {
+    fn id(&self) -> u32 {
+        self.row * 8 + self.col
+    }
+}
+
+impl FromStr for Seat {
+    type Err = Error;
+
+    fn from_str(s: &str) -> Result<Self> {
+        let row = s.chars().take(7).try_fold(0..128, |range, c| match c {
+            'F' => Ok(range.start..(range.end - ((range.end - range.start) / 2))),
+            'B' => Ok((range.start + ((range.end - range.start) / 2))..range.end),
+            _ => Err(anyhow!("Unrecognized row character: {}", c)),
+        })?;
+        let col = s
+            .chars()
+            .skip(7)
+            .take(3)
+            .try_fold(0..8, |range, c| match c {
+                'L' => Ok(range.start..(range.end - ((range.end - range.start) / 2))),
+                'R' => Ok((range.start + ((range.end - range.start) / 2))..range.end),
+                _ => Err(anyhow!("Unrecognized row character: {}", c)),
+            })?;
+        Ok(Self {
+            row: row.start,
+            col: col.start,
+        })
+    }
+}
+
+fn solve_part1(input_path: &str) -> Result<u32> {
+    let file = File::open(input_path)?;
+    let reader = BufReader::new(file);
+
+    Ok(reader
+        .lines()
+        .map(|line| Seat::from_str(&line.unwrap()).unwrap())
+        .map(|seat| seat.id())
+        .max()
+        .ok_or(anyhow!("No seats found in input"))?)
+}
+
+fn solve_part2(input_path: &str) -> Result<u32> {
+    let file = File::open(input_path)?;
+    let reader = BufReader::new(file);
+    let mut seat_ids: Vec<u32> = reader
+        .lines()
+        .map(|line| Seat::from_str(&line.unwrap()).unwrap())
+        .map(|seat| seat.id())
+        .collect();
+    seat_ids.sort_unstable();
+
+    let mut prev_seat = None;
+    for seat_id in seat_ids {
+        if let Some(prev_seat) = prev_seat {
+            if seat_id != prev_seat + 1 {
+                return Ok(prev_seat + 1);
+            }
+        }
+        prev_seat = Some(seat_id);
+    }
+
+    Err(anyhow!("No missing seat was found in input"))
+}
+
+fn main() {
+    println!("Part 1: {}", solve_part1(INPUT).unwrap());
+    println!("Part 2: {}", solve_part2(INPUT).unwrap());
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    const TEST_INPUT: &str = "input/test.txt";
+
+    #[test]
+    fn parses_input() {
+        let file = File::open(TEST_INPUT).unwrap();
+        let reader = BufReader::new(file);
+        let seats: Vec<Seat> = reader
+            .lines()
+            .map(|line| Seat::from_str(&line.unwrap()))
+            .collect::<Result<Vec<Seat>>>()
+            .unwrap();
+        assert_eq!(seats[0], Seat { row: 70, col: 7 });
+        assert_eq!(seats[0].id(), 567);
+        assert_eq!(seats[1], Seat { row: 14, col: 7 });
+        assert_eq!(seats[1].id(), 119);
+        assert_eq!(seats[2], Seat { row: 102, col: 4 });
+        assert_eq!(seats[2].id(), 820);
+    }
+
+    #[test]
+    fn solves_part1() {
+        assert_eq!(solve_part1(TEST_INPUT).unwrap(), 820);
+    }
+
+    #[test]
+    fn solves_part2() {
+        assert_eq!(solve_part2(TEST_INPUT).unwrap(), 120);
+    }
+}