disable day 14 part 2 because it requires manual intervention

src/day12.rs

@@ -56,12 +56,12 @@ fn part2(input: &str) -> RiddleResult {
         }
         let mut area = 0;
         let mut further = vec![p];
-        let mut convex_corners = 0;
+        let mut group = HashSet::new();
-        let mut concave_corners = 0;
         while let Some(current) = further.pop() {
             if processed.contains(&current) {
                 continue;
             }
+            group.insert(current);
             area += 1;
             for next in NEIGHBORS.iter().map(|d| (current.0 + d.0, current.1 + d.1)) {
                 let next_c = garden.get(next);
@@ -71,28 +71,88 @@ fn part2(input: &str) -> RiddleResult {
                 }
             }
             processed.insert(current);
-            for (da, db) in NEIGHBORS.iter().circular_tuple_windows() {
-                let a = (current.0 + da.0, current.1 + da.1);
-                let b = (current.0 + db.0, current.1 + db.1);
-                if garden.get(a) != Some(c) && garden.get(b) != Some(c) {
-                    convex_corners += 1;
-                } else if garden.get(a) == Some(c)
-                    && garden.get(b) == Some(c)
-                    && garden.get((current.0 + da.0 + db.0, current.1 + da.1 + db.1)) != Some(c)
-                {
-                    concave_corners += 1;
-                }
-            }
         }
-        let var_name = convex_corners + concave_corners;
+        result += area * sides(group);
-        let var_name = area * (var_name);
-        result += var_name;
     }
     result
 }
 
+fn sides(group: HashSet<(i64, i64)>) -> RiddleResult {
+    let x_range = group.iter().min_by_key(|it| it.0).unwrap().0
+        ..=group.iter().max_by_key(|it| it.0).unwrap().0;
+    let y_range = group.iter().min_by_key(|it| it.1).unwrap().1
+        ..=group.iter().max_by_key(|it| it.1).unwrap().1;
+    let mut result = 0;
+    for x in x_range {
+        // 1 for the ending of the last group, +1 for each time a line "stops", e.g. between the current point and next there is a gap
+        let points = group
+            .iter()
+            .filter(|p| p.0 == x)
+            .filter(|p| !group.contains(&(p.0 - 1, p.1)))
+            .sorted_by_key(|p| p.1)
+            .collect_vec();
+        if !points.is_empty() {
+            let count = points
+                .into_iter()
+                .tuple_windows()
+                .filter(|(a, b)| a.1 + 1 != b.1)
+                .count();
+            result += 1 + count;
+        }
+        let points = group
+            .iter()
+            .filter(|p| p.0 == x)
+            .filter(|p| !group.contains(&(p.0 + 1, p.1)))
+            .sorted_by_key(|p| p.1)
+            .collect_vec();
+        if !points.is_empty() {
+            let count = points
+                .into_iter()
+                .tuple_windows()
+                .filter(|(a, b)| a.1 + 1 != b.1)
+                .count();
+            result += 1 + count;
+        }
+    }
+    for y in y_range {
+        let points = group
+            .iter()
+            .filter(|p| p.1 == y)
+            .filter(|p| !group.contains(&(p.0, p.1 - 1)))
+            .sorted_by_key(|p| p.0)
+            .collect_vec();
+        if !points.is_empty() {
+            let count = points
+                .into_iter()
+                .tuple_windows()
+                .filter(|(a, b)| a.0 + 1 != b.0)
+                .count();
+            result += 1 + count;
+        }
+        let points = group
+            .iter()
+            .filter(|p| p.1 == y)
+            .filter(|p| !group.contains(&(p.0, p.1 + 1)))
+            .sorted_by_key(|p| p.0)
+            .collect_vec();
+        if !points.is_empty() {
+            let count = points
+                .into_iter()
+                .tuple_windows()
+                .filter(|(a, b)| a.0 + 1 != b.0)
+                .count();
+            result += 1 + count;
+        }
+    }
+    result as RiddleResult
+}
+
 #[cfg(test)]
 mod test {
+    use std::collections::HashSet;
+
+    use crate::day12::sides;
+
     use super::{part1, part2};
 
     const TEST_INPUT: &str = r"AAAA
@@ -110,4 +170,16 @@ EEEC
     fn test2() {
         assert_eq!(part2(TEST_INPUT), 80);
     }
+
+    #[test]
+    fn sides_one() {
+        let group = HashSet::from_iter([(3, 5)]);
+        assert_eq!(sides(group), 4);
+    }
+
+    #[test]
+    fn sides_plus() {
+        let group = HashSet::from_iter([(3, 3), (3, 4), (3, 2), (2, 3), (4, 3)]);
+        assert_eq!(sides(group), 12);
+    }
 }

src/day13.rs

@@ -0,0 +1,99 @@
+use std::fs::read_to_string;
+
+use itertools::Itertools;
+use regex::Regex;
+
+pub fn day_main() {
+    let input = read_to_string("input/day13.txt").unwrap();
+    let input = input.trim();
+    println!(" part1: {}", part1(input));
+    println!(" part2: {}", part2(input));
+}
+
+type RiddleResult = i64;
+
+fn part1(input: &str) -> RiddleResult {
+    // Button A: X+30, Y+84
+    // Button B: X+74, Y+60
+    // Prize: X=2358, Y=2628
+    let r = Regex::new(
+        r"Button A: X\+(\d+), Y\+(\d+)
+Button B: X\+(\d+), Y\+(\d+)
+Prize: X=(\d+), Y=(\d+)",
+    )
+    .unwrap();
+    r.captures_iter(input)
+        .map(|block| {
+            let (ax, ay, bx, by, px, py) = block
+                .iter()
+                .skip(1)
+                .map(|it| it.unwrap().as_str().parse::<i64>().unwrap())
+                .collect_tuple()
+                .unwrap();
+            solve((ax, ay, bx, by, px, py)).unwrap_or(0)
+        })
+        .sum()
+}
+
+fn part2(input: &str) -> RiddleResult {
+    let r = Regex::new(
+        r"Button A: X\+(\d+), Y\+(\d+)
+Button B: X\+(\d+), Y\+(\d+)
+Prize: X=(\d+), Y=(\d+)",
+    )
+    .unwrap();
+    r.captures_iter(input)
+        .map(|block| {
+            let (ax, ay, bx, by, px, py) = block
+                .iter()
+                .skip(1)
+                .map(|it| it.unwrap().as_str().parse::<i64>().unwrap())
+                .collect_tuple()
+                .unwrap();
+            let solution = solve((ax, ay, bx, by, px + 10000000000000, py + 10000000000000));
+            solution.unwrap_or(0)
+        })
+        .sum()
+}
+
+fn solve((ax, ay, bx, by, px, py): (i64, i64, i64, i64, i64, i64)) -> Option<RiddleResult> {
+    let b = (ay * px - ax * py) / (ay * bx - ax * by);
+    let a = (px - b * bx) / ax;
+    if a >= 0 && b >= 0 && a * ax + b * bx == px && a * ay + b * by == py {
+        Some(3 * a + b)
+    } else {
+        None
+    }
+}
+
+#[cfg(test)]
+mod test {
+    use super::{part1, part2};
+
+    const TEST_INPUT: &str = r"Button A: X+94, Y+34
+Button B: X+22, Y+67
+Prize: X=8400, Y=5400
+
+Button A: X+26, Y+66
+Button B: X+67, Y+21
+Prize: X=12748, Y=12176
+
+Button A: X+17, Y+86
+Button B: X+84, Y+37
+Prize: X=7870, Y=6450
+
+Button A: X+69, Y+23
+Button B: X+27, Y+71
+Prize: X=18641, Y=10279
+";
+
+    #[test]
+    fn test1() {
+        assert_eq!(part1(TEST_INPUT), 480);
+    }
+
+    #[test]
+    fn test2() {
+        assert_eq!(part2(TEST_INPUT), 875318608908);
+    }
+}

src/day14.rs

@@ -0,0 +1,156 @@
+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));
+    // 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();
+
+    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()
+}
+
+#[allow(unused)]
+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!()
+}
+
+type Robot = ((i64, i64), (i64, i64));
+
+fn printr(robots: &[Robot], 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

@@ -10,5 +10,7 @@ pub mod day09;
 pub mod day10;
 pub mod day11;
 pub mod day12;
+pub mod day13;
+pub mod day14;
 // PLACEHOLDER
 pub mod utils;

src/main.rs

@@ -17,6 +17,8 @@ fn main() {
         (10, day10::day_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());