day13

src/day13.rs

@@ -0,0 +1,76 @@
+use aoc_runner_derive::{aoc, aoc_generator};
+use itertools::Itertools;
+#[aoc_generator(day13, part1)]
+fn parse(input: &str) -> (i32, Vec<i32>) {
+    let (start, buses) = input
+        .lines()
+        .collect_tuple()
+        .unwrap();
+
+    let buses = buses
+        .split(',')
+        .filter_map(|num| num.parse::<i32>().ok())
+        .collect_vec();
+
+    (start.parse::<i32>().unwrap(), buses)
+}
+
+#[aoc(day13, part1)]
+fn part1((start, buses): &(i32, Vec<i32>)) -> i32 {
+    let mut cur = 0;
+    loop {
+        if let Some(bus) = buses.iter().find(|x| (cur + start) % *x == 0) {
+            return bus * cur;
+        }
+        cur += 1;
+    }
+}
+
+#[aoc_generator(day13, part2)]
+fn parse2(input: &str) -> Vec<Option<i64>> {
+    let buses = input
+        .lines().skip(1).next().unwrap();
+
+    let buses = buses
+        .split(',')
+        .map(|num| num.parse::<i64>().ok())
+        .collect_vec();
+
+    buses
+}
+
+#[aoc(day13, part2)]
+fn part2(input: &Vec<Option<i64>>) -> i64 {
+    let mut min_value = 0;
+    let mut running_product = 1;
+
+    for (index, bus) in input.iter().enumerate() {
+        if let Some(bus) = bus {
+            while (min_value + index as i64) % bus != 0 {
+                min_value += running_product;
+            }
+            running_product *= bus;
+        }
+    }
+
+    min_value
+}
+
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+const EX: &str = r"939
+7,13,x,x,59,x,31,19";
+
+    #[test]
+    fn part1_example() {
+        assert_eq!(part1(&parse(EX)), 295);
+    }
+
+    #[test]
+    fn part2_example() {
+        assert_eq!(part2(&parse2(EX)), 1068781);
+    }
+}

src/lib.rs

@@ -1,3 +1,4 @@
+mod day13;
 mod day12;
 mod day10;
 mod day9;