[2025] Day 3 solve + cleanup forgot to commit right after solving oops

Author: connorslade

README.md

@@ -7,6 +7,7 @@ Thank you to [Eric Wastl](http://was.tl) for running this incredible yearly even
 
 - [Day 01: Secret Entrance](aoc_2025/src/day_01.rs)
 - [Day 02: Gift Shop](aoc_2025/src/day_02.rs)
+- [Day 03: Lobby](aoc_2025/src/day_03.rs)
 <!-- MARKER -->
 
 ## [2024](https://adventofcode.com/2024) [![aoc_2024](https://github.com/connorslade/advent-of-code/actions/workflows/aoc_2024.yml/badge.svg)](https://github.com/connorslade/advent-of-code/actions/workflows/aoc_2024.yml)

aoc_2025/src/day_02.rs

@@ -43,8 +43,8 @@ fn count_invalid(input: &str, is_invalid: fn(u64) -> bool) -> u64 {
 
     for range in input.split(',') {
         let (start, end) = range.split_once('-').unwrap();
-        let start = start.parse::<u64>().unwrap();
-        let end = end.parse::<u64>().unwrap();
+        let start = start.parse().unwrap();
+        let end = end.parse().unwrap();
 
         for id in start..=end {
             count += is_invalid(id) as u64 * id;

aoc_2025/src/day_03.rs

@@ -0,0 +1,66 @@
+use common::{Answer, solution};
+
+solution!("Lobby", 3);
+
+fn part_a(input: &str) -> Answer {
+    solve(input, 2).into()
+}
+
+fn part_b(input: &str) -> Answer {
+    solve(input, 12).into()
+}
+
+fn solve(input: &str, n: usize) -> u64 {
+    let mut out = 0;
+    for bank in input.trim().lines() {
+        let digits = bank
+            .chars()
+            .map(|x| x.to_digit(10).unwrap() as u8)
+            .collect::<Vec<_>>();
+        out += joltage(&digits, n);
+    }
+
+    out
+}
+
+fn joltage(digits: &[u8], n: usize) -> u64 {
+    let mut num = 0;
+    let mut last_used = 0;
+
+    for bat in 0..n {
+        let size = digits.len() - (n - 1 - bat) - last_used;
+        let slice = &digits[last_used..(last_used + size).min(digits.len())];
+
+        for i in (0..=9).rev() {
+            if let Some(idx) = slice.iter().position(|x| *x == i) {
+                last_used += idx + 1;
+                num = num * 10 + i as u64;
+                break;
+            }
+        }
+    }
+
+    num
+}
+
+#[cfg(test)]
+mod test {
+    use indoc::indoc;
+
+    const CASE: &str = indoc! {"
+        987654321111111
+        811111111111119
+        234234234234278
+        818181911112111
+    "};
+
+    #[test]
+    fn part_a() {
+        assert_eq!(super::part_a(CASE), 357.into());
+    }
+
+    #[test]
+    fn part_b() {
+        assert_eq!(super::part_b(CASE), 3121910778619_u64.into());
+    }
+}

aoc_2025/src/lib.rs

@@ -2,10 +2,12 @@ use common::Solution;
 
 mod day_01;
 mod day_02;
+mod day_03;
 // [import_marker]
 
 pub const SOLUTIONS: &[Solution] = &[
     day_01::SOLUTION,
     day_02::SOLUTION,
+    day_03::SOLUTION,
     // [list_marker]
 ];