1 files changed, 88 insertions, 0 deletions
diff --git a/2022/src/bin/day_4.rs b/2022/src/bin/day_4.rs
new file mode 100644
index 0000000..5f08d70
--- /dev/null
+++ b/2022/src/bin/day_4.rs
@@ -0,0 +1,88 @@
+use nom::{
+    bytes::complete::tag,
+    character::complete::{line_ending, u32 as nom_u32},
+    combinator::map,
+    multi::separated_list1,
+    sequence::tuple,
+    IResult,
+};
+use std::{fs, iter::Iterator, ops::RangeInclusive};
+
+fn main() -> Result<(), Box<dyn std::error::Error>> {
+    let input = fs::read_to_string("inputs/day_4.txt")?;
+    let assignments = Assignments::parser(&input).unwrap().1;
+    dbg!(assignments.count_containing_assignments());
+    dbg!(assignments.count_overlapping_assignments());
+    Ok(())
+}
+
+#[derive(Debug, PartialEq, Eq, Clone)]
+struct Assignments(Vec<AssignmentPair>);
+
+#[derive(Debug, PartialEq, Eq, Clone)]
+struct AssignmentPair {
+    elf_1: Assignment,
+    elf_2: Assignment,
+}
+
+#[derive(Debug, PartialEq, Eq, Clone)]
+struct Assignment(RangeInclusive<u32>);
+
+impl Assignments {
+    fn parser(input: &str) -> IResult<&str, Assignments> {
+        map(
+            separated_list1(line_ending, AssignmentPair::parser),
+            Assignments,
+        )(input)
+    }
+
+    fn count_containing_assignments(&self) -> usize {
+        self.0
+            .iter()
+            .filter(|pair| pair.one_completely_overlaps_other())
+            .count()
+    }
+
+    fn count_overlapping_assignments(&self) -> usize {
+        self.0
+            .iter()
+            .filter(|pair| pair.one_overlaps_other())
+            .count()
+    }
+}
+
+impl AssignmentPair {
+    fn parser(input: &str) -> IResult<&str, AssignmentPair> {
+        map(
+            tuple((Assignment::parser, tag(","), Assignment::parser)),
+            |(elf_1, _, elf_2)| AssignmentPair { elf_1, elf_2 },
+        )(input)
+    }
+
+    fn one_completely_overlaps_other(&self) -> bool {
+        self.elf_1.contains(&self.elf_2) || self.elf_2.contains(&self.elf_1)
+    }
+
+    fn one_overlaps_other(&self) -> bool {
+        self.elf_1.overlaps(&self.elf_2)
+    }
+}
+
+impl Assignment {
+    fn parser(input: &str) -> IResult<&str, Assignment> {
+        map(tuple((nom_u32, tag("-"), nom_u32)), |(start, _, end)| {
+            Assignment(RangeInclusive::new(start, end))
+        })(input)
+    }
+
+    fn contains(&self, other: &Assignment) -> bool {
+        self.0.contains(other.0.start()) && self.0.contains(other.0.end())
+    }
+
+    fn overlaps(&self, other: &Assignment) -> bool {
+        self.0.contains(other.0.start())
+            || self.0.contains(other.0.end())
+            || other.0.contains(self.0.start())
+            || other.0.contains(self.0.end())
+    }
+}