diff --git a/day16/src/claude.rs b/day16/src/claude.rs
new file mode 100644
index 0000000..934b875
--- /dev/null
+++ b/day16/src/claude.rs
@@ -0,0 +1,72 @@
+use regex::Regex;
+use std::collections::HashMap;
+use std::fs;
+
+/// One remembered Aunt Sue: her number and whatever compounds were noted.
+#[derive(Debug)]
+struct Sue {
+    number: u32,
+    properties: HashMap<String, u32>,
+}
+
+/// Parses the puzzle input into a list of `Sue`s.
+///
+/// Each line looks like `Sue 1: goldfish: 9, cars: 0, samoyeds: 9`. The
+/// number of properties varies per line, so we pull out the `name: count`
+/// pairs with a regex rather than assuming a fixed format.
+fn parse_sues(input: &str) -> Vec<Sue> {
+    let line_re = Regex::new(r"^Sue (\d+): (.+)$").unwrap();
+    let property_re = Regex::new(r"(\w+): (\d+)").unwrap();
+
+    input
+        .lines()
+        .filter_map(|line| {
+            let caps = line_re.captures(line)?;
+            let number = caps[1].parse().unwrap();
+            let properties = property_re
+                .captures_iter(&caps[2])
+                .map(|prop| (prop[1].to_string(), prop[2].parse().unwrap()))
+                .collect();
+
+            Some(Sue { number, properties })
+        })
+        .collect()
+}
+
+/// The exact readings from the MFCSAM.
+fn target_properties() -> HashMap<&'static str, u32> {
+    HashMap::from([
+        ("children", 3),
+        ("cats", 7),
+        ("samoyeds", 2),
+        ("pomeranians", 3),
+        ("akitas", 0),
+        ("vizslas", 0),
+        ("goldfish", 5),
+        ("trees", 3),
+        ("cars", 2),
+        ("perfumes", 1),
+    ])
+}
+
+/// A Sue matches if every compound she's remembered for equals the target
+/// reading exactly. Properties she isn't remembered for are simply skipped,
+/// per the puzzle's "missing things aren't zero" rule.
+fn matches_target(sue: &Sue, target: &HashMap<&str, u32>) -> bool {
+    sue.properties
+        .iter()
+        .all(|(name, &count)| target.get(name.as_str()) == Some(&count))
+}
+
+fn main() {
+    let input = fs::read_to_string("input.txt").expect("failed to read input.txt");
+    let sues = parse_sues(&input);
+    let target = target_properties();
+
+    let real_sue = sues
+        .iter()
+        .find(|sue| matches_target(sue, &target))
+        .expect("no Sue matched the MFCSAM readings");
+
+    println!("Sue {} gave the gift.", real_sue.number);
+}