1 files changed, 62 insertions, 0 deletions
diff --git a/src/bin/day4.rs b/src/bin/day4.rs
new file mode 100644
index 0000000..93e7b20
--- /dev/null
+++ b/src/bin/day4.rs
@@ -0,0 +1,62 @@
+static DAY: u8 = 4;
+
+fn main() {
+    let input = advent::read_lines(DAY);
+    println!("{DAY}a: {}", overlaps(&input, true));
+    println!("{DAY}b: {}", overlaps(&input, false));
+}
+
+struct Range {
+    start: u32,
+    end: u32,
+}
+
+impl Range {
+    fn new(input: &str) -> Range {
+        let (start, end) = input.split_once('-').unwrap();
+        let start = start.parse::<u32>().unwrap();
+        let end = end.parse::<u32>().unwrap();
+        Range { start, end }
+    }
+
+    fn overlaps(&self, other: &Range, fully_contained: bool) -> bool {
+        if fully_contained {
+            self.start <= other.start && self.end >= other.end
+        } else {
+            self.start <= other.start && self.end >= other.start
+        }
+    }
+}
+
+fn overlaps(input: &[String], fully_contained: bool) -> u32 {
+    let mut count = 0;
+    for line in input {
+        let (range1, range2) = line.split_once(',').unwrap();
+        let range1 = Range::new(range1);
+        let range2 = Range::new(range2);
+        if range1.overlaps(&range2, fully_contained) || range2.overlaps(&range1, fully_contained) {
+            count += 1;
+        }
+    }
+    count
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test() {
+        let input = [
+            "2-4,6-8".to_string(),
+            "2-3,4-5".to_string(),
+            "5-7,7-9".to_string(),
+            "2-8,3-7".to_string(),
+            "6-6,4-6".to_string(),
+            "2-6,4-8".to_string(),
+        ];
+
+        assert_eq!(overlaps(&input, true), 2);
+        assert_eq!(overlaps(&input, false), 4);
+    }
+}