Implementation day 6

2020/samples/06.txt

@@ -0,0 +1,15 @@
+abc
+
+a
+b
+c
+
+ab
+ac
+
+a
+a
+a
+a
+
+b

2020/src/day06.rs

@@ -1,12 +1,72 @@
 use std::io::Read;
 
+use crate::common::read_single_input;
 use crate::Solution;
 
+type Answers = u32;
+
+fn count(answers: Answers) -> u32 {
+    answers.count_ones()
+}
+
+fn compute_answers(group: &str) -> Answers {
+    let mut questions = 0;
+
+    for question in group.chars().filter(char::is_ascii_lowercase) {
+        questions |= 1 << (question as usize - 'a' as usize);
+    }
+
+    questions
+}
+
+fn count_answers_all(group: &str) -> u32 {
+    let mut combined = 0xffff_ffff;
+
+    for line in group.split('\n') {
+        let single = compute_answers(line);
+
+        combined &= single;
+    }
+
+    count(combined)
+}
+
 #[derive(Default)]
 pub struct Day06;
 
 impl Solution for Day06 {
     fn part1(&mut self, input: &mut dyn Read) -> String {
-        todo!()
+        let input: String = read_single_input(input);
+
+        let total: u32 = input.split("\n\n").map(compute_answers).map(count).sum();
+
+        total.to_string()
+    }
+
+    fn part2(&mut self, input: &mut dyn Read) -> String {
+        let input: String = read_single_input(input);
+
+        let total: u32 = input.split("\n\n").map(count_answers_all).sum();
+
+        total.to_string()
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::test_implementation;
+
+    use super::*;
+
+    const SAMPLE: &[u8] = include_bytes!("../samples/06.txt");
+
+    #[test]
+    fn sample_part1() {
+        test_implementation!(Day06, 1, SAMPLE, 11);
+    }
+
+    #[test]
+    fn sample_part2() {
+        test_implementation!(Day06, 2, SAMPLE, 6);
     }
 }