diff --git a/2022/Cargo.lock b/2022/Cargo.lock
index 5cceaa4..4eabd40 100644
--- a/2022/Cargo.lock
+++ b/2022/Cargo.lock
@@ -2,6 +2,31 @@
 # It is not intended for manual editing.
 version = 3
 
+[[package]]
+name = "memchr"
+version = "2.5.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "2dffe52ecf27772e601905b7522cb4ef790d2cc203488bbd0e2fe85fcb74566d"
+
+[[package]]
+name = "minimal-lexical"
+version = "0.2.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "68354c5c6bd36d73ff3feceb05efa59b6acb7626617f4962be322a825e61f79a"
+
+[[package]]
+name = "nom"
+version = "7.1.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "a8903e5a29a317527874d0402f867152a3d21c908bb0b933e416c65e301d4c36"
+dependencies = [
+ "memchr",
+ "minimal-lexical",
+]
+
 [[package]]
 name = "problems"
 version = "0.1.0"
+dependencies = [
+ "nom",
+]
diff --git a/2022/Cargo.toml b/2022/Cargo.toml
index 7bf1070..fb3d37e 100644
--- a/2022/Cargo.toml
+++ b/2022/Cargo.toml
@@ -6,3 +6,4 @@ edition = "2021"
 # See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
 
 [dependencies]
+nom = { version = "7" }
diff --git a/2022/data/day4.txt b/2022/data/day4.txt
new file mode 100644
index 0000000..107893a
--- /dev/null
+++ b/2022/data/day4.txt
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diff --git a/2022/src/day4.rs b/2022/src/day4.rs
new file mode 100644
index 0000000..336ad76
--- /dev/null
+++ b/2022/src/day4.rs
@@ -0,0 +1,150 @@
+use nom::{self, bytes::complete::tag, character::complete, sequence::separated_pair, IResult};
+use std::collections::HashSet;
+
+const INPUT: &str = include_str!("../data/day4.txt");
+
+pub fn part1() -> String {
+    format!("{}", count_full_containments(input(INPUT)))
+}
+
+pub fn part2() -> String {
+    format!("{}", count_overlaps(input(INPUT)))
+}
+
+fn count_full_containments(pairings: Vec<ElfPairing>) -> u32 {
+    pairings.into_iter().fold(0, |cur, pairing| {
+        if pairing.has_full_containment() {
+            cur + 1
+        } else {
+            cur
+        }
+    })
+}
+
+fn count_overlaps(pairings: Vec<ElfPairing>) -> u32 {
+    pairings.into_iter().fold(
+        0,
+        |cur, pairing| {
+            if pairing.has_overlap() {
+                cur + 1
+            } else {
+                cur
+            }
+        },
+    )
+}
+
+struct ElfPairing {
+    elf1: Vec<u32>,
+    elf2: Vec<u32>,
+}
+
+impl ElfPairing {
+    fn has_full_containment(&self) -> bool {
+        let elf1 = self.elf1.iter().cloned().collect::<HashSet<u32>>();
+        let elf2 = self.elf2.iter().cloned().collect::<HashSet<u32>>();
+        elf1.is_subset(&elf2) || elf2.is_subset(&elf1)
+    }
+
+    fn has_overlap(&self) -> bool {
+        let element_count = self.elf1.len() + self.elf2.len();
+        let combined_set = self
+            .elf1
+            .iter()
+            .chain(self.elf2.iter())
+            .cloned()
+            .collect::<HashSet<u32>>();
+        combined_set.len() < element_count
+    }
+}
+
+fn input(data: &str) -> Vec<ElfPairing> {
+    data.lines()
+        .map(|line| {
+            let (_, pairing) = elf_pair(line).unwrap();
+            pairing
+        })
+        .collect::<Vec<ElfPairing>>()
+}
+
+fn elf_pair(input: &str) -> IResult<&str, ElfPairing> {
+    let (input, elf1) = elf_range(input)?;
+    let (input, _) = tag(",")(input)?;
+    let (input, elf2) = elf_range(input)?;
+
+    Ok((input, ElfPairing { elf1, elf2 }))
+}
+
+fn elf_range(input: &str) -> IResult<&str, Vec<u32>> {
+    let (input, start) = complete::u32(input)?;
+    let (input, _) = tag("-")(input)?;
+    let (input, end) = complete::u32(input)?;
+
+    Ok((input, (start..end + 1).collect::<Vec<u32>>()))
+}
+
+#[cfg(test)]
+mod test {
+    use super::*;
+
+    const TEST_DATA: &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 it_gets_a_hashset_from_a_range() {
+        assert_eq!(vec![2, 3, 4], (2..5).collect::<Vec<u32>>());
+    }
+
+    fn with_input<F>(test: F)
+    where
+        F: Fn(Vec<ElfPairing>) -> () + std::panic::UnwindSafe,
+    {
+        test(input(TEST_DATA));
+    }
+
+    #[test]
+    fn it_parses_input_correctly() {
+        with_input(|pairings| {
+            assert_eq!(vec![2, 3, 4], pairings[0].elf1);
+            assert_eq!(vec![6, 7, 8], pairings[0].elf2);
+
+            assert_eq!(vec![6], pairings[4].elf1);
+            assert_eq!(vec![4, 5, 6], pairings[4].elf2);
+        });
+    }
+
+    #[test]
+    fn it_checks_full_containment() {
+        with_input(|pairings| {
+            assert!(!pairings[0].has_full_containment());
+            assert!(!pairings[1].has_full_containment());
+            assert!(!pairings[2].has_full_containment());
+            assert!(pairings[3].has_full_containment());
+            assert!(pairings[4].has_full_containment());
+            assert!(!pairings[5].has_full_containment());
+        });
+    }
+
+    #[test]
+    fn it_counts_full_containments() {
+        with_input(|pairings| {
+            assert_eq!(2, count_full_containments(pairings));
+        });
+    }
+
+    #[test]
+    fn it_checks_overlap() {
+        with_input(|pairings| {
+            assert!(!pairings[0].has_overlap());
+            assert!(!pairings[1].has_overlap());
+            assert!(pairings[2].has_overlap());
+            assert!(pairings[3].has_overlap());
+            assert!(pairings[4].has_overlap());
+            assert!(pairings[5].has_overlap());
+        });
+    }
+}
diff --git a/2022/src/main.rs b/2022/src/main.rs
index b2586bf..f7e89a5 100644
--- a/2022/src/main.rs
+++ b/2022/src/main.rs
@@ -1,6 +1,7 @@
 mod day1;
 mod day2;
 mod day3;
+mod day4;
 
 fn main() {
     let day = std::env::args().skip(1).next();
@@ -12,6 +13,8 @@ fn main() {
         Some("2b") => day2::part2(),
         Some("3a") => day3::part1(),
         Some("3b") => day3::part2(),
+        Some("4a") => day4::part1(),
+        Some("4b") => day4::part2(),
         _ => panic!("unrecognized day"),
     };