Implementation day 5

2020/src/day05.rs

@@ -0,0 +1,54 @@
+use std::io::BufRead;
+use std::io::BufReader;
+use std::io::Read;
+
+use crate::Solution;
+
+fn seat_id(boarding_pass: &str) -> u32 {
+    boarding_pass
+        .chars()
+        .fold(0, |b, c| (b << 1) | ((c == 'B' || c == 'R') as u32))
+}
+
+fn seat_iter<'a>(input: &'a mut dyn Read) -> impl Iterator<Item = u32> + 'a {
+    BufReader::new(input).lines().map(|s| seat_id(&s.unwrap()))
+}
+
+#[derive(Default)]
+pub struct Day05;
+
+impl Solution for Day05 {
+    fn part1(&mut self, input: &mut dyn Read) -> String {
+        seat_iter(input).max().unwrap().to_string()
+    }
+
+    fn part2(&mut self, input: &mut dyn Read) -> String {
+        let mut taken = [false; 0x3ff];
+
+        for seat_id in seat_iter(input) {
+            taken[seat_id as usize] = true;
+        }
+
+        let pattern = [true, false, true];
+
+        for (i, window) in taken.windows(3).enumerate() {
+            if window == pattern {
+                return (i + 1).to_string();
+            }
+        }
+
+        panic!("No seat found!");
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_seat_id() {
+        assert_eq!(567, seat_id("BFFFBBFRRR"));
+        assert_eq!(119, seat_id("FFFBBBFRRR"));
+        assert_eq!(820, seat_id("BBFFBBFRLL"));
+    }
+}

2020/src/lib.rs

@@ -5,6 +5,7 @@ mod day01;
 mod day02;
 mod day03;
 mod day04;
+mod day05;
 
 pub trait Solution {
     fn part1(&mut self, input: &mut dyn Read) -> String;
@@ -20,6 +21,7 @@ pub fn get_implementation(day: usize) -> Box<dyn Solution> {
         2 => Box::new(day02::Day02::default()),
         3 => Box::new(day03::Day03::default()),
         4 => Box::new(day04::Day04::default()),
+        5 => Box::new(day05::Day05::default()),
         _ => panic!("Unsupported day {}", day),
     }
 }