2020: day05: part 1

aoc2020/src/day05.rs

@@ -0,0 +1,108 @@
+use std::fmt::Write;
+use std::str::FromStr;
+
+use aoc::err;
+
+const INPUT: &str = include_str!("../input/day05.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 seats = input
+        .lines()
+        .map(|line| line.parse())
+        .collect::<aoc::Result<Vec<Seat>>>()
+        .map_err(|e| err!("{}", e))?;
+
+    seats
+        .iter()
+        .map(|seat| seat.id())
+        .max()
+        .ok_or_else(|| err!("0 seats processed"))
+}
+
+#[derive(Debug, PartialEq, Eq)]
+struct Seat {
+    row: usize,
+    column: usize,
+}
+
+impl Seat {
+    fn id(&self) -> usize {
+        self.row * 8 + self.column
+    }
+}
+
+impl FromStr for Seat {
+    type Err = aoc::Error;
+
+    fn from_str(s: &str) -> aoc::Result<Self> {
+        if s.len() != 10 {
+            return Err(err!("Seat encoding must be 10 chars long: {}", s));
+        }
+
+        let (mut row_begin, mut row_end) = (0, 128);
+        let (mut col_begin, mut col_end) = (0, 8);
+        for c in s.chars() {
+            let row_range = (row_end - row_begin) / 2;
+            let col_range = (col_end - col_begin) / 2;
+            match c {
+                'B' => {
+                    row_begin += row_range;
+                }
+                'F' => {
+                    row_end -= row_range;
+                }
+                'L' => {
+                    col_end -= col_range;
+                }
+                'R' => {
+                    col_begin += col_range;
+                }
+                _ => return Err(err!("Wrong char while decoding seat: `{}`", c)),
+            }
+        }
+
+        Ok(Self {
+            row: row_begin,
+            column: col_begin,
+        })
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn part1_provided() {
+        let seat: Seat = "BFFFBBFRRR".parse().unwrap();
+        assert_eq!(seat, Seat { row: 70, column: 7 });
+        assert_eq!(seat.id(), 567);
+
+        let seat: Seat = "FFFBBBFRRR".parse().unwrap();
+        assert_eq!(seat, Seat { row: 14, column: 7 });
+        assert_eq!(seat.id(), 119);
+
+        let seat: Seat = "BBFFBBFRLL".parse().unwrap();
+        assert_eq!(
+            seat,
+            Seat {
+                row: 102,
+                column: 4
+            }
+        );
+        assert_eq!(seat.id(), 820);
+    }
+
+    #[test]
+    fn part1_real() {
+        assert_eq!(part1(INPUT).unwrap(), 850);
+    }
+}

aoc2020/src/lib.rs

@@ -2,3 +2,4 @@ pub mod day01;
 pub mod day02;
 pub mod day03;
 pub mod day04;
+pub mod day05;

aoc2020/src/main.rs

@@ -5,9 +5,10 @@ use aoc2020::day01;
 use aoc2020::day02;
 use aoc2020::day03;
 use aoc2020::day04;
+use aoc2020::day05;
 
 fn main() -> Result<()> {
-    let days: &[DayFunc] = &[day01::run, day02::run, day03::run, day04::run];
+    let days: &[DayFunc] = &[day01::run, day02::run, day03::run, day04::run, day05::run];
 
     aoc::run(days)
 }