day 20

src/bin/day20_1.rs

@@ -0,0 +1,8 @@
+use std::fs;
+
+use aoc2022::day20::process_part_1;
+
+fn main() {
+    let file = fs::read_to_string("./inputs/day20.txt").unwrap();
+    println!("{}", process_part_1(&file));
+}

src/bin/day20_2.rs

@@ -0,0 +1,8 @@
+use std::fs;
+
+use aoc2022::day20::process_part_2;
+
+fn main() {
+    let file = fs::read_to_string("./inputs/day20.txt").unwrap();
+    println!("{}", process_part_2(&file));
+}

src/day20.rs

@@ -0,0 +1,69 @@
+use itertools::Itertools;
+use nom::character::complete;
+use nom::character::complete::newline;
+use nom::multi::separated_list1;
+use nom::IResult;
+
+pub fn process_part_1(input: &str) -> i64 {
+    let values = parse_input(input).unwrap().1;
+    let mixed = mix(&values, 1);
+    let zero_pos = mixed.iter().position(|&v| v == 0).unwrap();
+
+    [1000, 2000, 3000]
+        .into_iter()
+        .map(|pos| mixed[(zero_pos + pos) % mixed.len()])
+        .sum()
+}
+
+pub fn process_part_2(input: &str) -> i64 {
+    let values = parse_input(input).unwrap().1;
+    let values = values.into_iter().map(|v| v * 811589153).collect_vec();
+    let mixed = mix(&values, 10);
+    let zero_pos = mixed.iter().position(|&v| v == 0).unwrap();
+
+    [1000, 2000, 3000]
+        .into_iter()
+        .map(|pos| mixed[(zero_pos + pos) % mixed.len()])
+        .sum()
+}
+
+fn mix(values: &[i64], rounds: usize) -> Vec<i64> {
+    let mut indices = (0..values.len()).collect::<Vec<_>>();
+    for _ in 0..rounds {
+        for (i, &v) in values.iter().enumerate() {
+            let pos = indices.iter().position(|&index| index == i).unwrap();
+            let removed = indices.remove(pos);
+            let new_pos = ((pos as i64) + v).rem_euclid(values.len() as i64 - 1) as usize;
+            indices.insert(new_pos, removed);
+        }
+    }
+    // reconstruct using mixed indices
+    indices.iter().map(|&i| values[i]).collect()
+}
+
+fn parse_input(input: &str) -> IResult<&str, Vec<i64>> {
+    separated_list1(newline, complete::i64)(input)
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    const INPUT: &str = "1
+2
+-3
+3
+-2
+0
+4";
+
+    #[test]
+    fn day1() {
+        assert_eq!(process_part_1(INPUT), 3);
+    }
+
+    #[test]
+    fn day2() {
+        assert_eq!(process_part_2(INPUT), 1623178306);
+    }
+}

src/lib.rs

@@ -20,3 +20,4 @@ pub mod day16;
 pub mod day17;
 pub mod day18;
 pub mod day19;
+pub mod day20;