day 4

src/day04.rs

@@ -0,0 +1,74 @@
+use nom::IResult;
+use std::ops::RangeInclusive;
+
+pub fn process_part_1(input: &str) -> usize {
+    let (_, assignments) = section_assignments(input).unwrap();
+    assignments
+        .iter()
+        .filter(|(a, b)| range_contains(a, b) || range_contains(b, a))
+        .count()
+}
+
+pub fn process_part_2(input: &str) -> usize {
+    let (_, assignments) = section_assignments(input).unwrap();
+    assignments
+        .iter()
+        .filter(|(a, b)| a.clone().into_iter().any(|n| b.contains(&n)))
+        .count()
+}
+
+fn range_contains(haystack: &RangeInclusive<u32>, needle: &RangeInclusive<u32>) -> bool {
+    haystack.contains(needle.start()) && haystack.contains(needle.end())
+}
+
+fn section_assignments(
+    input: &str,
+) -> IResult<&str, Vec<(RangeInclusive<u32>, RangeInclusive<u32>)>> {
+    use nom::character::complete::newline;
+    use nom::multi::separated_list1;
+
+    let (input, ranges) = separated_list1(newline, line)(input)?;
+    Ok((input, ranges))
+}
+
+fn line(input: &str) -> IResult<&str, (RangeInclusive<u32>, RangeInclusive<u32>)> {
+    use nom::bytes::complete::tag;
+
+    let (input, start) = sections(input)?;
+    let (input, _) = tag(",")(input)?;
+    let (input, end) = sections(input)?;
+    Ok((input, (start, end)))
+}
+
+fn sections(input: &str) -> IResult<&str, RangeInclusive<u32>> {
+    use nom::bytes::complete::tag;
+    use nom::character::complete;
+
+    let (input, start) = complete::u32(input)?;
+    let (input, _) = tag("-")(input)?;
+    let (input, end) = complete::u32(input)?;
+
+    Ok((input, start..=end))
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    const INPUT: &str = "2-4,6-8
+2-3,4-5
+5-7,7-9
+2-8,3-7
+6-6,4-6
+2-6,4-8";
+
+    #[test]
+    fn day1() {
+        assert_eq!(process_part_1(INPUT), 2);
+    }
+
+    #[test]
+    fn day2() {
+        assert_eq!(process_part_2(INPUT), 4);
+    }
+}