[2025] Day 2 first solution

Author: connorslade

README.md

@@ -6,6 +6,7 @@ Thank you to [Eric Wastl](http://was.tl) for running this incredible yearly even
 ## [2025](https://adventofcode.com/2025) [![aoc_2025](https://github.com/connorslade/advent-of-code/actions/workflows/aoc_2025.yml/badge.svg)](https://github.com/connorslade/advent-of-code/actions/workflows/aoc_2025.yml)
 
 - [Day 01: Secret Entrance](aoc_2025/src/day_01.rs)
+- [Day 02: Gift Shop](aoc_2025/src/day_02.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

@@ -0,0 +1,85 @@
+use common::{Answer, solution};
+
+solution!("Gift Shop", 2);
+
+fn part_a(input: &str) -> Answer {
+    let mut count = 0;
+
+    for range in input.trim().split(',') {
+        let (start, end) = range.split_once('-').unwrap();
+        let start = start.parse::<u64>().unwrap();
+        let end = end.parse::<u64>().unwrap();
+
+        for id in start..=end {
+            count += is_invalid(id) as u64 * id;
+        }
+    }
+
+    count.into()
+}
+
+fn part_b(input: &str) -> Answer {
+    let mut count = 0;
+
+    for range in input.trim().split(',') {
+        let (start, end) = range.split_once('-').unwrap();
+        let start = start.parse::<u64>().unwrap();
+        let end = end.parse::<u64>().unwrap();
+
+        for id in start..=end {
+            count += is_invalid2(id) as u64 * id;
+        }
+    }
+
+    count.into()
+}
+
+fn is_invalid(id: u64) -> bool {
+    let digits = (id.ilog10() + 1) / 2;
+    let mask = 10_u64.pow(digits);
+    id % mask == id / mask
+}
+
+fn is_invalid2(id: u64) -> bool {
+    let digits = id.ilog10() + 1;
+
+    'outer: for size in 1..=(digits / 2) {
+        let mask = 10_u64.pow(size);
+        let repeated = id % mask;
+        if (digits / size) * size != digits || repeated == 0 || repeated.ilog10() + 1 != size {
+            continue;
+        }
+
+        let mut id = id;
+        for _ in 0..(digits / size) {
+            if id % mask != repeated {
+                continue 'outer;
+            }
+
+            id /= mask;
+        }
+
+        return true;
+    }
+
+    false
+}
+
+#[cfg(test)]
+mod test {
+    use indoc::indoc;
+
+    const CASE: &str = indoc! {"
+        11-22,95-115,998-1012,1188511880-1188511890,222220-222224,1698522-1698528,446443-446449,38593856-38593862,565653-565659,824824821-824824827,2121212118-2121212124
+    "};
+
+    #[test]
+    fn part_a() {
+        assert_eq!(super::part_a(CASE), 1227775554.into());
+    }
+
+    #[test]
+    fn part_b() {
+        assert_eq!(super::part_b(CASE), 4174379265_u64.into());
+    }
+}

aoc_2025/src/lib.rs

@@ -1,9 +1,11 @@
 use common::Solution;
 
 mod day_01;
+mod day_02;
 // [import_marker]
 
 pub const SOLUTIONS: &[Solution] = &[
     day_01::SOLUTION,
+    day_02::SOLUTION,
     // [list_marker]
 ];