1 files changed, 92 insertions, 0 deletions
diff --git a/2020/rust/day06/src/main.rs b/2020/rust/day06/src/main.rs
new file mode 100644
index 0000000..948276a
--- /dev/null
+++ b/2020/rust/day06/src/main.rs
@@ -0,0 +1,92 @@
+use anyhow::Result;
+use std::collections::HashSet;
+use std::env::args;
+use std::fs::File;
+use std::io::{BufRead, BufReader};
+use std::path::Path;
+
+fn read_input<T: AsRef<Path>>(filename: T) -> Result<Vec<Vec<String>>> {
+    let f = File::open(filename)?;
+    let reader = BufReader::new(f);
+    let mut group = vec![];
+    let mut groups = vec![];
+
+    for line in reader.lines() {
+        let line = line?;
+        if line.is_empty() {
+            groups.push(group);
+            group = vec![];
+            continue;
+        }
+        group.push(line);
+    }
+    groups.push(group);
+
+    Ok(groups)
+}
+
+fn part1(input: &[Vec<String>]) -> Option<usize> {
+    let mut groups = vec![];
+    for group in input {
+        let mut set = HashSet::new();
+        for form in group.iter() {
+            for answer in form.clone().drain(..) {
+                set.insert(answer);
+            }
+        }
+        groups.push(set);
+    }
+    Some(groups.iter().map(|g| g.len()).sum())
+}
+
+fn part2(input: &[Vec<String>]) -> Option<usize> {
+    let mut groups = vec![];
+    for group in input {
+        let sets: Vec<_> = group.iter().map(|form| {
+            let mut set = HashSet::new();
+            for answer in form.clone().drain(..) {
+                set.insert(answer);
+            }
+            set
+        }).collect();
+        let combined: HashSet<_> = match sets.get(0) {
+            Some(first) => sets.iter()
+                .fold(first.clone(), |a, s| s.intersection(&a).cloned().collect()),
+            None => return None,
+        };
+
+        groups.push(combined);
+    }
+    Some(groups.iter().map(|g| g.len()).sum())
+}
+
+fn main() {
+    let (do_part_1, do_part_2) = aoc::do_parts();
+
+    let filename = match args().nth(1) {
+        Some(f) => f,
+        None => {
+            eprintln!("Missing input filename");
+            std::process::exit(1);
+        },
+    };
+    match read_input(filename) {
+        Ok(input) => {
+            if do_part_1 {
+                match part1(&input) {
+                    Some(solution) =>
+                        println!("Part1, sum of all groups combined yes answers: {}", solution),
+                    None => eprintln!("Part1, no soluton found"),
+                }
+            }
+            if do_part_2 {
+                match part2(&input) {
+                    Some(solution) =>
+                        println!("Part2, sum of all groups common yes answers: {}", solution),
+                    None => eprintln!("Part2, no soluton found"),
+                }
+            }
+        },
+        Err(err) => eprintln!("Could not read input: {}", err),
+    }
+}