day6

src/bin/day6.rs

@@ -0,0 +1,76 @@
+const INPUT: &str = include_str!("../../data/day6/input");
+
+#[derive(Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Debug)]
+struct Answers {
+	mask: u32,
+}
+
+impl Answers {
+	fn parse(data: &str) -> Self {
+		let data = data.trim();
+		let mask = data.chars().map(|c| {
+			let c = c as u32;
+			assert!(c < 0x80);
+			let c = c as u8;
+			assert!(c >= b'a' && c <= b'z');
+			let c = c - b'a';
+			c
+		}).fold(0, |mask, bit| {
+			mask | 1 << bit
+		});
+		Self { mask }
+	}
+
+	fn count(&self) -> u32 {
+		self.mask.count_ones()
+	}
+}
+
+impl std::ops::BitOr for Answers {
+	type Output = Self;
+
+	fn bitor(self, rhs: Self) -> Self::Output {
+		Self { mask: self.mask | rhs.mask }
+	}
+}
+
+impl std::ops::BitAnd for Answers {
+	type Output = Self;
+
+	fn bitand(self, rhs: Self) -> Self::Output {
+		Self { mask: self.mask & rhs.mask }
+	}
+}
+
+struct Group {
+	answers: Vec<Answers>,
+}
+
+impl Group {
+	fn parse(input: &str) -> Vec<Self> {
+		input.split("\n\n").map(|block| {
+			let answers = block.lines().map(Answers::parse).collect();
+			Group { answers }
+		}).collect()
+	}
+
+	fn any_answered(&self) -> Answers {
+		self.answers.iter().fold(Answers { mask: 0 }, |a, &b| a | b)
+	}
+
+	fn all_answered(&self) -> Answers {
+		self.answers[1..].iter().fold(self.answers[0], |a, &b| a & b)
+	}
+}
+
+fn main() {
+	let groups = Group::parse(INPUT);
+	println!(
+		"Sum of questions answered yes at least one per group: {}",
+		groups.iter().map(|g| g.any_answered().count()).sum::<u32>(),
+	);
+	println!(
+		"Sum of questions answered yes by everyone per group: {}",
+		groups.iter().map(|g| g.all_answered().count()).sum::<u32>(),
+	);
+}