2024 day8

aoc_utils/Cargo.toml

@@ -4,3 +4,4 @@ version = "0.1.0"
 edition = "2021"
 
 [dependencies]
+num-traits = "0.2.19"

aoc_utils/src/lib.rs

@@ -1,5 +1,7 @@
+use num_traits::{zero, PrimInt};
 use std::collections::{HashMap, HashSet};
 use std::fs::read_to_string;
+use std::ops::RemAssign;
 
 pub fn read_lines(filename: &str) -> Vec<String> {
     read_to_string(filename)
@@ -62,3 +64,16 @@ pub fn primes(number: &u32) -> impl Iterator<Item = u32> {
 
     (2..n + 1).filter(move |&i| !&sieve.contains(&i))
 }
+
+pub fn gcd<T: PrimInt + RemAssign>(mut n: T, mut m: T) -> T {
+    let zero = T::zero();
+
+    assert!(n != zero && m != zero);
+    while m != zero {
+        if m < n {
+            std::mem::swap(&mut m, &mut n);
+        }
+        m %= n;
+    }
+    n
+}

year_2024/input/day8.txt

@@ -0,0 +1,50 @@
+..................................................
+.r................................................
+..........................I.......................
+........................I.........................
+................................................M.
+............h......................A..............
+..7....................I.........h................
+......7..................................M....9...
+.o.....U..........................................
+......................................O...........
+....c.................J................O...M...A..
+..................................................
+...R...7..........................................
+..............r...................................
+...................J..................9...........
+...7..K......UJ...................................
+......0...U.........................x.............
+.......R.......0..B......................x........
+.......................k.....Z.......9............
+.......L.........I.....J............m.............
+.....K.BR........r.0.C............................
+.......K.BR......c................................
+..................h....m....Al...........H........
+..............L..k.......h...m..........x..9......
+........................Z.....m........xO.........
+..........0................l......................
+.6..................b.............................
+............k...o..............Z..................
+........4.....o...........L.......................
+....................Xo............................
+...........8..B..L.........i......................
+..z...............bX..........A...................
+j........z...X......C.......i........5............
+.b...H6.......................U.......l...........
+..................X...............................
+...6......................Z..........a............
+....6........c............5.........1.............
+.4.......................5........................
+..........k.......H1l.............................
+2.................C.......i...................u...
+.............a....2...............................
+.....z....H.......1..8.....................u......
+...........j...b..................................
+3.........j.........................a.............
+...4................a.............................
+..M................j.....1..........5.............
+............................................u.....
+..4..3...........i................................
+z3.................2..............................
+..........8..................2.C..................

year_2024/src/day8.rs

@@ -0,0 +1,119 @@
+use std::collections::{HashMap, HashSet};
+use std::ops::{Add, RemAssign};
+
+pub fn execute() -> String {
+    let data = aoc_utils::read_lines("input/day8.txt");
+    let city = City::from_lines(data);
+
+    let part1 = city.find_antinodes(false).len();
+    let part2 = city.find_antinodes(true).len();
+
+    format!("{} {}", part1, part2)
+}
+
+struct City {
+    size: isize,
+    antennas: HashMap<char, Vec<(isize, isize)>>,
+}
+
+impl City {
+    fn from_lines(lines: Vec<String>) -> City {
+        let size = lines.len() as isize;
+
+        let mut antennas = HashMap::new();
+        for (j, line) in lines.iter().enumerate() {
+            assert_eq!(line.len() as isize, size);
+            for (i, c) in line.chars().enumerate() {
+                if c != '.' {
+                    antennas
+                        .entry(c)
+                        .or_insert_with(Vec::new)
+                        .push((i as isize, j as isize));
+                }
+            }
+        }
+
+        City { size, antennas }
+    }
+
+    fn find_antinodes(&self, part2: bool) -> HashSet<(isize, isize)> {
+        let mut result = HashSet::new();
+        for (_freq, positions) in self.antennas.iter() {
+            for a in positions {
+                for b in positions {
+                    if a == b {
+                        continue;
+                    }
+                    let d = (b.0 - a.0, b.1 - a.1);
+
+                    let (start, step) = if part2 {
+                        let dtemp = d.clone();
+                        let gcd = aoc_utils::gcd(dtemp.0.abs(), dtemp.1.abs());
+                        (a, (d.0 / gcd, d.1 / gcd))
+                    } else {
+                        (b, d)
+                    };
+
+                    let mut c = start.clone();
+                    loop {
+                        c.0 += step.0;
+                        c.1 += step.1;
+
+                        if c.0 < 0 || c.0 >= self.size || c.1 < 0 || c.1 >= self.size {
+                            break;
+                        }
+                        result.insert(c.clone());
+                        if !part2 {
+                            break;
+                        }
+                    }
+                }
+            }
+        }
+        result
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_mine() {
+        assert_eq!(execute(), String::from("259 927"));
+    }
+
+    #[test]
+    fn test_from_lines() {
+        let city = City::from_lines(_example());
+        assert_eq!(city.size, 12);
+        assert_eq!(city.antennas.len(), 2);
+        assert_eq!(city.antennas[&'0'].len(), 4);
+        assert_eq!(city.antennas[&'A'].len(), 3);
+    }
+
+    #[test]
+    fn test_find_antinodes() {
+        let city = City::from_lines(_example());
+
+        assert_eq!(city.find_antinodes(false).len(), 14);
+        assert_eq!(city.find_antinodes(true).len(), 34);
+    }
+
+    fn _example() -> Vec<String> {
+        vec![
+            String::from("............"),
+            String::from("........0..."),
+            String::from(".....0......"),
+            String::from(".......0...."),
+            String::from("....0......."),
+            String::from("......A....."),
+            String::from("............"),
+            String::from("............"),
+            String::from("........A..."),
+            String::from(".........A.."),
+            String::from("............"),
+            String::from("............"),
+        ]
+    }
+}

year_2024/src/main.rs

@@ -6,6 +6,7 @@ mod day4;
 mod day5;
 mod day6;
 mod day7;
+mod day8;
 
 fn main() {
     println!("Day  1: {}", day1::execute());
@@ -15,4 +16,5 @@ fn main() {
     println!("Day  5: {}", day5::execute());
     println!("Day  6: {}", day6::execute());
     println!("Day  7: {}", day7::execute());
+    println!("Day  8: {}", day8::execute());
 }