From 1821c48f4431d34cea9006566d01c4bef60698b9 Mon Sep 17 00:00:00 2001
From: Jeremy Kaplan <jdkaplan@metagram.net>
Date: Sat, 3 Dec 2022 21:33:03 -0800
Subject: [PATCH] 2022 Day 4

---
 2022/src/bin/day04.rs | 77 +++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 77 insertions(+)
 create mode 100644 2022/src/bin/day04.rs

diff --git a/2022/src/bin/day04.rs b/2022/src/bin/day04.rs
new file mode 100644
index 0000000..a1e5333
--- /dev/null
+++ b/2022/src/bin/day04.rs
@@ -0,0 +1,77 @@
+use std::str::FromStr;
+
+const INPUT: &str = include_str!("../../input/day04.txt");
+
+fn main() {
+    println!("{}", part1(INPUT));
+    println!("{}", part2(INPUT));
+}
+
+#[derive(Debug, Copy, Clone)]
+struct Assignment {
+    start: usize,
+    end: usize,
+}
+
+impl FromStr for Assignment {
+    type Err = std::convert::Infallible; // just trust me
+
+    fn from_str(s: &str) -> Result<Self, Self::Err> {
+        let parts: Vec<&str> = s.split('-').collect();
+        let start: usize = parts[0].parse().unwrap();
+        let end: usize = parts[1].parse().unwrap();
+        Ok(Self { start, end })
+    }
+}
+
+impl Assignment {
+    fn contains(&self, other: Self) -> bool {
+        self.start <= other.start && other.end <= self.end
+    }
+
+    fn overlaps(&self, other: Self) -> bool {
+        self.contains(other) || other.contains(*self)
+    }
+
+    fn intersect(&self, other: Self) -> Option<Self> {
+        use std::cmp::{max, min};
+        let start = max(self.start, other.start);
+        let end = min(self.end, other.end);
+
+        if start <= end {
+            Some(Self { start, end })
+        } else {
+            None
+        }
+    }
+
+    fn intersects(&self, other: Self) -> bool {
+        self.intersect(other).is_some()
+    }
+}
+
+fn part1(input: &str) -> usize {
+    parse_input(input)
+        .iter()
+        .filter(|(l, r)| l.overlaps(*r))
+        .count()
+}
+
+fn parse_input(input: &str) -> Vec<(Assignment, Assignment)> {
+    input
+        .split('\n')
+        .filter(|l| !l.is_empty())
+        .map(|line| {
+            let parts: Vec<&str> = line.split(',').collect();
+            let l = Assignment::from_str(parts[0]).unwrap();
+            let r = Assignment::from_str(parts[1]).unwrap();
+            (l, r)
+        })
+        .collect()
+}
+
+fn part2(input: &str) -> usize {
+    let pairs = parse_input(input);
+
+    pairs.iter().filter(|(l, r)| l.intersects(*r)).count()
+}