day15

src/day15.rs

@@ -0,0 +1,60 @@
+use std::collections::HashMap;
+
+use aoc_runner_derive::{aoc, aoc_generator};
+use itertools::Itertools;
+
+
+#[aoc_generator(day15)]
+fn parse(input: &str) -> Vec<u64> {
+    input.split(',').map(str::parse::<u64>).map(Result::unwrap).collect_vec()
+}
+
+#[aoc(day15, part1)]
+fn part1(input: &Vec<u64>) -> u64 {
+    let mut list = input.iter().take(input.len() - 1).cloned().enumerate().map(|(i,v)| (v,i)).collect::<HashMap<_, _>>();
+    let mut cur = *input.last().unwrap();
+
+    for turn in input.len() - 1..2020 - 1 {
+        let mut next = 0;
+        if let Some(last_turn) = list.get_mut(&cur) {
+            next = (turn - *last_turn) as u64;
+        }
+        list.insert(cur, turn);
+        cur = next;
+    }
+    cur
+}
+
+#[aoc(day15, part2)]
+fn part2(input: &Vec<u64>) -> u64 {
+    let mut list = input.iter().take(input.len() - 1).cloned().enumerate().map(|(i,v)| (v,i)).collect::<HashMap<_, _>>();
+    let mut cur = *input.last().unwrap();
+
+    for turn in input.len() - 1..30000000 - 1 {
+        let mut next = 0;
+        if let Some(last_turn) = list.get_mut(&cur) {
+            next = (turn - *last_turn) as u64;
+        }
+        list.insert(cur, turn);
+        cur = next;
+    }
+    cur
+}
+
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    const EX: &str = r"0,3,6";
+
+    #[test]
+    fn part1_example() {
+        assert_eq!(part1(&parse(EX)), 436);
+    }
+
+    #[test]
+    fn part2_example() {
+        assert_eq!(part2(&parse(EX)), 175594);
+    }
+}

src/lib.rs

@@ -1,3 +1,4 @@
+mod day15;
 mod day14;
 mod day13;
 mod day12;