2024: Add solution to Day 10

Author: dcoles

2024/Cargo.lock

@@ -19,7 +19,7 @@ cargo run --bin day01
 7. [Bridge Repair](day07) 🌟🌟
 8. [Resonant Collinearity](day08) 🌟🌟
 9. [Disk Fragmenter](day09) 🌟🌟
-10. [](day10)
+10. [Hoof It](day10) 🌟🌟
 11. [](day11)
 12. [](day12)
 13. [](day13)

2024/README.md

@@ -6,3 +6,4 @@ edition = "2021"
 # See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
 
 [dependencies]
+lib = { path = "../lib" }

2024/day10/Cargo.toml

@@ -0,0 +1,4 @@
+0123
+1234
+8765
+9876

2024/day10/example1.txt

@@ -0,0 +1,7 @@
+...0...
+...1...
+...2...
+6543456
+7.....7
+8.....8
+9.....9

2024/day10/example2.txt

@@ -0,0 +1,8 @@
+89010123
+78121874
+87430965
+96549874
+45678903
+32019012
+01329801
+10456732

2024/day10/example5.txt

@@ -0,0 +1,7 @@
+.....0.
+..4321.
+..5..2.
+..6543.
+..7..4.
+..8765.
+..9....

2024/day10/example6.txt

@@ -0,0 +1,7 @@
+..90..9
+...1.98
+...2..7
+6543456
+765.987
+876....
+987....

2024/day10/example7.txt

@@ -0,0 +1,53 @@
+65456780121098450187634569763232345103213014321223456
+56565097632787543296323478890141234234102125630310767
+67874198545601612345610165765650105145693496543407898
+32923238723432709654326543034789076008786587854343210
+41010129610549878723017832129878989019895674963210349
+03498034534698965014898901038965432123107895674310478
+12567012345787854198743230123453219654256456789321565
+01698107659834723085650134562104508723340349876459874
+98787238543225610176590121875698698812451210145960123
+07456549850110765203485430984788767904322109236871234
+12349654763234894312176534983109456765012218347120105
+45898763120125234523054325672112309876544367898034876
+36765812034576127654369010766043218987432458765565989
+29876903107681038923478001897652345898901089014877856
+10945789218996987610569123078901236754321198123966987
+89032654309345678510787430121230109865120567001855496
+70121023498210709425698945230381210778034056532743345
+63210110567601812334321876545496321689765123443412210
+54216787014503956745430965496587434509894329856301101
+09105496923212345866787634987676543213456018763456932
+18012387836781078975898523432345232122347890345367873
+27601078745896769784309410541230143021038901276216784
+34587669654305854693210305670321056523427987689105698
+03490548741214903543211234781987897012310094576543567
+12321239230903212650106521892016798987454123467612430
+12332102107812121786787430752105678901960013438900421
+01489237876543080695890124567234787017871012543321530
+90574323965012891234301233208943296323702387654487651
+87665010121026700343210120112350185410213498703599341
+96556901212345619656903234013461234554396569812678210
+03467832303434328743874105684570789689487876101432387
+12346345694540345012565106799688778776536964566501498
+01653210789691236522210239888799669890123453677890567
+18764101988780987121329845677234550187652122989108906
+89765001877101071030456776540112341290343001010267210
+67896982769612132549105689432101032301234578981354310
+78767853458743247678014988654312121000225665432458981
+69656765432658958976529812763243029810116767898567652
+30345899891067867789438701890156710723209852101438943
+21230014780890986290105610981260823654367643067324321
+10101423634761870121234327876501994569498543458015100
+45672344543052765436543234566782987678534412109176211
+34985495652143781287430110545093456767623303678989321
+43856784743430690398710325432112129865414510510076450
+32981012892121589459621234521001036772301623423165569
+01670143345023498764560149693456345681066739654234678
+12365294256510107643498238782347652397659848765985589
+03454385107898212532567345601098701498943707678876432
+12763476543789123431052101598709876510232110569845001
+29854307630076034521043015691612389323101023454032132
+38765218921165087654321126780543432134569878998108941
+47894356712234198765230105621234567023878565089237650
+21012349803343289890121234310123498012967432176546321

2024/day10/input.txt

@@ -2,11 +2,20 @@
 //! https://adventofcode.com/2024/day/10
 
 use std::{fs, io};
+use std::collections::{BTreeMap, BTreeSet};
 use std::path::Path;
+use lib::vector::Vector;
+
+type Vec2 = Vector<i32, 2>;
+
+const UP: Vec2 = Vec2::new([0, -1]);
+const DOWN: Vec2 = Vec2::new([0, 1]);
+const LEFT: Vec2 = Vec2::new([-1, 0]);
+const RIGHT: Vec2 = Vec2::new([1, 0]);
 
 fn main() {
-    let input = Input::from_file(format!("{}/input.txt", env!("CARGO_MANIFEST_DIR"))).expect("failed to read input");
-    //let input = Input::from_file(format!("{}/example1.txt", env!("CARGO_MANIFEST_DIR"))).expect("failed to read input");
+    //let input = Input::from_file(format!("{}/input.txt", env!("CARGO_MANIFEST_DIR"))).expect("failed to read input");
+    let input = Input::from_file(format!("{}/example5.txt", env!("CARGO_MANIFEST_DIR"))).expect("failed to read input");
     println!("{input:?}");
 
     // Part 1
@@ -17,24 +26,107 @@ fn main() {
 }
 
 fn part1(input: &Input) -> usize {
-    0
+    let trailheads: BTreeSet<Vec2> = input.heights.iter()
+        .filter_map(|(&p, &h)| (h == 0).then_some(p)).collect();
+
+    trailheads.into_iter().map(|head| score(head, &input.heights)).sum()
+}
+
+fn score(trailhead: Vec2, heights: &BTreeMap<Vec2, u8>) -> usize {
+    let mut score = 0;
+
+    let mut visited: BTreeSet<Vec2> = [trailhead].into_iter().collect();
+    let mut edge = vec![trailhead];
+
+    while let Some(pos) = edge.pop() {
+        let height = heights[&pos];
+
+        if height == 9 {
+            score += 1;
+            continue;
+        }
+
+        for dir in [UP, DOWN, LEFT, RIGHT] {
+            let next_pos = pos + dir;
+            if visited.contains(&next_pos) {
+                continue;
+            }
+
+            if heights.get(&next_pos).copied() == Some(height + 1) {
+                visited.insert(next_pos);
+                edge.push(next_pos);
+            }
+        }
+    }
+
+    score
 }
 
+
 fn part2(input: &Input) -> usize {
-    0
+    let trailheads: BTreeSet<Vec2> = input.heights.iter()
+        .filter_map(|(&p, &h)| (h == 0).then_some(p)).collect();
+
+    trailheads.into_iter().map(|head| rating(head, &input.heights)).sum()
+}
+
+fn rating(trailhead: Vec2, heights: &BTreeMap<Vec2, u8>) -> usize {
+    let mut rating = 0;
+
+    let mut visited: BTreeSet<Vec<Vec2>> = [vec![trailhead]].into_iter().collect();
+    let mut edge = vec![vec![trailhead]];
+
+    while let Some(trail) = edge.pop() {
+        let pos = *trail.last().unwrap();
+        let height = heights[&pos];
+        if height == 9 {
+            rating += 1;
+            continue;
+        }
+
+        for dir in [UP, DOWN, LEFT, RIGHT] {
+            let next_pos = pos + dir;
+            let new_trail: Vec<_> = trail.iter().copied().chain([next_pos]).collect();
+
+            if visited.contains(&new_trail) {
+                continue;
+            }
+
+            if heights.get(&next_pos).copied() == Some(height + 1) {
+                visited.insert(new_trail.clone());
+                edge.push(new_trail);
+            }
+        }
+    }
+
+    rating
 }
 
 #[derive(Debug, Clone)]
 struct Input {
-    values: Vec<String>,
+    heights: BTreeMap<Vec2, u8>,
 }
 
 impl Input {
     fn from_file(path: impl AsRef<Path>) -> io::Result<Self> {
         let input = fs::read_to_string(path)?;
-        let values = input.lines().map(str::to_string).collect();
 
-        Ok(Self { values })
+        let mut heights = BTreeMap::new();
+
+        for (x, line) in input.lines().enumerate() {
+            for (y, c) in line.trim().chars().enumerate() {
+                if c == '.' {
+                    continue;
+                }
+
+                let pos = Vec2::new([x as i32, y as i32]);
+                let height = c.to_digit(10).unwrap() as u8;
+
+                heights.insert(pos, height);
+            }
+        }
+
+        Ok(Self { heights })
     }
 }
 
@@ -44,29 +136,29 @@ mod test {
 
     #[test]
     fn test_part1() {
-        let input = Input::from_file("example1.txt").unwrap();
+        let input = Input::from_file("example5.txt").unwrap();
 
-        assert_eq!(part1(&input), 0);
+        assert_eq!(part1(&input), 36);
     }
 
     #[test]
     fn test_part1_solution() {
         let input = Input::from_file("input.txt").unwrap();
 
-        assert_eq!(part1(&input), 0);
+        assert_eq!(part1(&input), 776);
     }
 
     #[test]
     fn test_part2() {
-        let input = Input::from_file("example1.txt").unwrap();
+        let input = Input::from_file("example5.txt").unwrap();
 
-        assert_eq!(part2(&input), 0);
+        assert_eq!(part2(&input), 81);
     }
 
     #[test]
     fn test_part2_solution() {
         let input = Input::from_file("input.txt").unwrap();
 
-        assert_eq!(part2(&input), 0);
+        assert_eq!(part2(&input), 1657);
     }
 }