Day 03 solutions

Author: Cadiac

README.md

@@ -87,3 +87,5 @@ This should start the server at `localhost:8080`.
 ## Solutions
 
 ❄️ [Day 01](aoc-solver/src/y2025/day01.rs)
+❄️ [Day 02](aoc-solver/src/y2025/day02.rs)
+❄️ [Day 03](aoc-solver/src/y2025/day03.rs)

aoc-solver/src/y2025/day03.rs

@@ -0,0 +1,160 @@
+use crate::solution::{AocError, Solution};
+
+pub struct Day03;
+
+fn parse(input: &str) -> Result<Vec<Vec<u32>>, AocError> {
+    input
+        .trim()
+        .lines()
+        .map(|batteries| {
+            batteries
+                .chars()
+                .map(|battery| {
+                    battery
+                        .to_digit(10)
+                        .ok_or(AocError::parse(battery, "invalid joltage"))
+                })
+                .collect()
+        })
+        .collect()
+}
+
+fn find_max_joltage(banks: &[u32], digits: usize) -> u64 {
+    let mut skip = 0;
+    let mut result = 0;
+
+    for digit in 0..digits {
+        let digit_pos = digits - digit - 1;
+        let take = banks.len() - skip - digit_pos;
+
+        let mut banks_to_check = banks.iter().skip(skip).take(take);
+        let max = banks_to_check.clone().max().unwrap();
+
+        skip += banks_to_check.position(|battery| battery == max).unwrap() + 1;
+        result += 10u64.pow(digit_pos as u32) * *max as u64
+    }
+
+    result
+}
+
+impl Solution for Day03 {
+    type Part1 = u64;
+    type Part2 = u64;
+
+    fn default_input(&self) -> &'static str {
+        include_str!("../../../inputs/2025/day03.txt")
+    }
+
+    fn part_1(&self, input: &str) -> Result<u64, AocError> {
+        let total = parse(input)?
+            .iter()
+            .map(|bank| find_max_joltage(bank, 2))
+            .sum();
+
+        Ok(total)
+    }
+
+    fn part_2(&self, input: &str) -> Result<u64, AocError> {
+        let total = parse(input)?
+            .iter()
+            .map(|bank| find_max_joltage(bank, 12))
+            .sum();
+
+        Ok(total)
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn it_finds_max_joltage_1() {
+        assert_eq!(
+            find_max_joltage(&[9, 8, 7, 6, 5, 4, 3, 2, 1, 1, 1, 1, 1, 1, 1], 2),
+            98
+        );
+    }
+
+    #[test]
+    fn it_finds_max_joltage_2() {
+        assert_eq!(
+            find_max_joltage(&[8, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 9], 2),
+            89
+        )
+    }
+
+    #[test]
+    fn it_finds_max_joltage_3() {
+        assert_eq!(
+            find_max_joltage(&[2, 3, 4, 2, 3, 4, 2, 3, 4, 2, 3, 4, 2, 7, 8], 2),
+            78
+        )
+    }
+
+    #[test]
+    fn it_finds_max_joltage_4() {
+        assert_eq!(
+            find_max_joltage(&[8, 1, 8, 1, 8, 1, 9, 1, 1, 1, 1, 2, 1, 1, 1], 2),
+            92
+        )
+    }
+
+    #[test]
+    fn it_finds_max_joltage_5() {
+        assert_eq!(
+            find_max_joltage(&[9, 8, 7, 6, 5, 4, 3, 2, 1, 1, 1, 1, 1, 1, 1], 12),
+            987654321111
+        );
+    }
+
+    #[test]
+    fn it_finds_max_joltage_6() {
+        assert_eq!(
+            find_max_joltage(&[8, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 9], 12),
+            811111111119
+        );
+    }
+
+    #[test]
+    fn it_finds_max_joltage_7() {
+        assert_eq!(
+            find_max_joltage(&[2, 3, 4, 2, 3, 4, 2, 3, 4, 2, 3, 4, 2, 7, 8], 12),
+            434234234278
+        );
+    }
+
+    #[test]
+    fn it_finds_max_joltage_8() {
+        assert_eq!(
+            find_max_joltage(&[8, 1, 8, 1, 8, 1, 9, 1, 1, 1, 1, 2, 1, 1, 1], 12),
+            888911112111
+        );
+    }
+
+    #[test]
+    fn it_solves_part1_example() {
+        assert_eq!(
+            Day03.part_1(
+                "987654321111111\n\
+                 811111111111119\n\
+                 234234234234278\n\
+                 818181911112111"
+            ),
+            Ok(357)
+        );
+    }
+
+    #[test]
+    fn it_solves_part2_example() {
+        assert_eq!(
+            Day03.part_2(
+                "987654321111111\n\
+                 811111111111119\n\
+                 234234234234278\n\
+                 818181911112111"
+            ),
+            Ok(3121910778619)
+        );
+    }
+}

aoc-solver/src/y2025/mod.rs

@@ -2,8 +2,9 @@ use crate::solution::{Solution, Solver};
 
 pub mod day01;
 pub mod day02;
+pub mod day03;
 
-pub const MAX_DAYS: u8 = 2;
+pub const MAX_DAYS: u8 = 3;
 
 pub struct Y2025;
 
@@ -12,6 +13,7 @@ impl Solver for Y2025 {
         match day {
             1 => day01::Day01.run(input, 1, 2025),
             2 => day02::Day02.run(input, 2, 2025),
+            3 => day03::Day03.run(input, 3, 2025),
             _ => vec![String::from("Solution not implemented (yet?)")],
         }
     }
@@ -31,6 +33,7 @@ impl Solver for Y2025 {
         match day {
             1 => include_str!("./day01.rs"),
             2 => include_str!("./day02.rs"),
+            3 => include_str!("./day03.rs"),
             _ => unimplemented!(),
         }
     }

aoc-web/src/header.rs

@@ -21,6 +21,7 @@ pub fn header(props: &HeaderProps) -> Html {
                                 <>
                                     <NavLink route={Route::Solution { year: 2025, day: 1 }} current={props.route.clone()} text={"1"}/>
                                     <NavLink route={Route::Solution { year: 2025, day: 2 }} current={props.route.clone()} text={"2"}/>
+                                    <NavLink route={Route::Solution { year: 2025, day: 3 }} current={props.route.clone()} text={"3"}/>
                                 </>
                             }
                         },