2025 02.1

Author: Lexicality

data

@@ -0,0 +1,61 @@
+// Copyright (c) 2025 Lexi Robinson
+//
+// Licensed under the EUPL, Version 1.2
+//
+// You may not use this work except in compliance with the Licence.
+// You should have received a copy of the Licence along with this work. If not, see:
+// <https://joinup.ec.europa.eu/collection/eupl/eupl-text-eupl-12>.
+// See the Licence for the specific language governing permissions and limitations under the Licence.
+
+use std::ops::RangeInclusive;
+
+use itertools::Itertools;
+use num::Integer;
+
+use crate::AoCError;
+
+pub fn part_1(data: crate::DataIn) -> crate::AoCResult<String> {
+    // damn references
+    let lines = data.collect_vec();
+    let ranges: Vec<RangeInclusive<u64>> = lines
+        .iter()
+        .flat_map(|line| line.split(','))
+        .map(|raw| {
+            raw.split_once('-')
+                .ok_or_else(|| AoCError::new(format!("Line {raw} is missing a -!")))
+                .and_then(|(start, end)| Ok((start.parse()?)..=(end.parse()?)))
+        })
+        .try_collect()?;
+
+    log::debug!("Collected ranges: {ranges:?}");
+
+    let ret: u64 = ranges
+        .into_iter()
+        .flat_map(|range| {
+            range.filter(|num| {
+                let numstr = num.to_string();
+                // all invalid ids are a pair of numbers, so they must be even
+                if numstr.len().is_odd() {
+                    return false;
+                }
+                // safety: this string is made of numbers which are all going to be ascii
+                // characters unless something has gone catastrophically wrong
+                let (start, end) = numstr.split_at(numstr.len() / 2);
+                start == end
+            })
+        })
+        .inspect(|serial| log::debug!("Found invalid serial number {serial}"))
+        .sum();
+
+    Ok(ret.to_string())
+}
+
+inventory::submit!(crate::AoCDay {
+    year: "2025",
+    day: "2",
+    part_1: crate::AoCPart {
+        main: part_1,
+        example: part_1
+    },
+    part_2: None
+});

src/aoc/y2025/day02.rs

@@ -7,3 +7,4 @@
 // <https://joinup.ec.europa.eu/collection/eupl/eupl-text-eupl-12>.
 // See the Licence for the specific language governing permissions and limitations under the Licence.
 pub mod day01;
+pub mod day02;