day 14 part 2

src/day14.rs

@@ -0,0 +1,154 @@
+use std::{
+    collections::HashSet,
+    fs::read_to_string,
+    io::{self, BufRead},
+    ops::Sub,
+};
+
+use itertools::Itertools;
+
+pub fn day_main() {
+    let input = read_to_string("input/day14.txt").unwrap();
+    let input = input.trim();
+    println!(" part1: {}", part1(input)); // 50112000 too low
+    println!(" part2: {}", part2(input));
+}
+
+type RiddleResult = usize;
+
+fn part1(input: &str) -> RiddleResult {
+    solve_part1(input, 100, 101, 103)
+}
+
+fn solve_part1(input: &str, rounds: i64, width: i64, height: i64) -> RiddleResult {
+    let mut robots = parse(input);
+    for _ in 0..rounds {
+        robots.iter_mut().for_each(|((px, py), (vx, vy))| {
+            *px = (*px + width + *vx) % width;
+            *py = (*py + height + *vy) % height;
+        });
+    }
+    let upper_left = robots
+        .iter()
+        .filter(|&&((px, py), _)| px < width / 2 && py < height / 2)
+        .count();
+    let lower_left = robots
+        .iter()
+        .filter(|&&((px, py), _)| px < width / 2 && py > height / 2)
+        .count();
+    let upper_right = robots
+        .iter()
+        .filter(|&&((px, py), _)| px > width / 2 && py < height / 2)
+        .count();
+    let lower_right = robots
+        .iter()
+        .filter(|&&((px, py), _)| px > width / 2 && py > height / 2)
+        .count();
+
+    if upper_left + lower_left == upper_right + lower_right {}
+    upper_left * lower_left * upper_right * lower_right
+}
+
+fn parse(input: &str) -> Vec<((i64, i64), (i64, i64))> {
+    input
+        .lines()
+        .map(|line| {
+            line.strip_prefix("p=")
+                .unwrap()
+                .split(" v=")
+                .map(|s| {
+                    s.split(",")
+                        .map(|d| d.parse::<i64>().unwrap())
+                        .collect_tuple::<(i64, i64)>()
+                        .unwrap()
+                })
+                .collect_tuple()
+                .unwrap()
+        })
+        .collect_vec()
+}
+
+fn part2(input: &str) -> RiddleResult {
+    let width = 101;
+    let height = 103;
+    let mut robots = parse(input);
+    let mut seen = HashSet::new();
+    for second in 0.. {
+        if seen.contains(&robots) {
+            panic!("Loop after {second} rounds, but no christmas tree!");
+        }
+        seen.insert(robots.clone());
+        robots.iter_mut().for_each(|((px, py), (vx, vy))| {
+            *px = (*px + width + *vx) % width;
+            *py = (*py + height + *vy) % height;
+        });
+
+        if robots
+            .iter()
+            .filter(|(s, _)| {
+                robots
+                    .iter()
+                    .any(|(t, _)| t != s && (t.0.sub(s.0).abs() + t.1.sub(s.1).abs()) <= 2)
+            })
+            .count()
+            > robots.len() * 70 / 100
+        {
+            printr(&robots, width, height);
+            println!("after {} seconds. Press enter to continue or type 'merry christmas' if you can spot a tree!", second + 1); //+1 because we look at it after they have changed
+            let stdin = io::stdin();
+            let line = stdin.lock().lines().next().unwrap().unwrap();
+            if line.as_str().eq_ignore_ascii_case("merry christmas") {
+                return second + 1;
+            }
+        }
+    }
+    unreachable!()
+}
+
+fn printr(robots: &[((i64, i64), (i64, i64))], width: i64, height: i64) {
+    for y in 0..height {
+        for x in 0..width {
+            let c = robots
+                .iter()
+                .filter(|&&((px, py), _)| px == x && py == y)
+                .count();
+            if c == 0 {
+                print!(".");
+            } else {
+                print!("{c}");
+            }
+        }
+        println!();
+    }
+}
+
+#[cfg(test)]
+mod test {
+    use crate::day14::solve_part1;
+
+    use super::part2;
+
+    const TEST_INPUT: &str = r"p=0,4 v=3,-3
+p=6,3 v=-1,-3
+p=10,3 v=-1,2
+p=2,0 v=2,-1
+p=0,0 v=1,3
+p=3,0 v=-2,-2
+p=7,6 v=-1,-3
+p=3,0 v=-1,-2
+p=9,3 v=2,3
+p=7,3 v=-1,2
+p=2,4 v=2,-3
+p=9,5 v=-3,-3
+";
+
+    #[test]
+    fn test1() {
+        assert_eq!(solve_part1(TEST_INPUT, 100, 11, 7), 12);
+    }
+
+    #[test]
+    fn test2() {
+        assert_eq!(part2(TEST_INPUT), 0);
+    }
+}

src/lib.rs

@@ -11,5 +11,6 @@ pub mod day10;
 pub mod day11;
 pub mod day12;
 pub mod day13;
+pub mod day14;
 // PLACEHOLDER
 pub mod utils;

src/main.rs

@@ -18,6 +18,7 @@ fn main() {
         (11, day11::day_main),
         (12, day12::day_main),
         (13, day13::day_main),
+        (14, day14::day_main),
         // PLACEHOLDER
     ]);
     let day: Option<u8> = args().nth(1).and_then(|a| a.parse().ok());