Complete day 6

day-6/.gitignore

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+/target/

day-6/Cargo.lock

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+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+[[package]]
+name = "day-6"
+version = "0.1.0"
+dependencies = [
+ "indoc",
+]
+
+[[package]]
+name = "indoc"
+version = "0.3.6"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "47741a8bc60fb26eb8d6e0238bbb26d8575ff623fdc97b1a2c00c050b9684ed8"
+dependencies = [
+ "indoc-impl",
+ "proc-macro-hack",
+]
+
+[[package]]
+name = "indoc-impl"
+version = "0.3.6"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "ce046d161f000fffde5f432a0d034d0341dc152643b2598ed5bfce44c4f3a8f0"
+dependencies = [
+ "proc-macro-hack",
+ "proc-macro2",
+ "quote",
+ "syn",
+ "unindent",
+]
+
+[[package]]
+name = "proc-macro-hack"
+version = "0.5.19"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "dbf0c48bc1d91375ae5c3cd81e3722dff1abcf81a30960240640d223f59fe0e5"
+
+[[package]]
+name = "proc-macro2"
+version = "1.0.24"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "1e0704ee1a7e00d7bb417d0770ea303c1bccbabf0ef1667dae92b5967f5f8a71"
+dependencies = [
+ "unicode-xid",
+]
+
+[[package]]
+name = "quote"
+version = "1.0.7"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "aa563d17ecb180e500da1cfd2b028310ac758de548efdd203e18f283af693f37"
+dependencies = [
+ "proc-macro2",
+]
+
+[[package]]
+name = "syn"
+version = "1.0.53"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "8833e20724c24de12bbaba5ad230ea61c3eafb05b881c7c9d3cfe8638b187e68"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "unicode-xid",
+]
+
+[[package]]
+name = "unicode-xid"
+version = "0.2.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "f7fe0bb3479651439c9112f72b6c505038574c9fbb575ed1bf3b797fa39dd564"
+
+[[package]]
+name = "unindent"
+version = "0.1.7"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "f14ee04d9415b52b3aeab06258a3f07093182b88ba0f9b8d203f211a7a7d41c7"

day-6/Cargo.toml

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+[package]
+name = "day-6"
+version = "0.1.0"
+authors = ["Tristan Daniël Maat <tm@tlater.net>"]
+edition = "2018"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]
+indoc = "0.3"

day-6/src/main.rs

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+use std::collections::HashSet;
+use std::fs;
+
+fn main() -> Result<(), Box<dyn std::error::Error>> {
+    let input = fs::read_to_string("input")?;
+
+    // Part 1
+    let groups = parse_groups(&input)?;
+    println!("{}", count_answers(&groups));
+
+    // Part 2
+    let groups = parse_group_individuals(&input)?;
+    println!("{}", count_individual_answers(&groups));
+
+    Ok(())
+}
+
+fn parse_groups(input: &str) -> Result<Vec<HashSet<char>>, String> {
+    input
+        .split("\n\n")
+        .map(|group| {
+            group
+                .chars()
+                .filter(|c| *c != '\n')
+                .map(|c| {
+                    if c.is_alphabetic() {
+                        Ok(c)
+                    } else {
+                        Err(format!("Invalid answer: {}", c))
+                    }
+                })
+                .collect()
+        })
+        .collect()
+}
+
+fn count_answers(groups: &Vec<HashSet<char>>) -> usize {
+    groups.iter().map(|group| group.iter().count()).sum()
+}
+
+fn parse_group_individuals(input: &str) -> Result<Vec<Vec<HashSet<char>>>, String> {
+    input
+        .split("\n\n")
+        .map(|group| {
+            group
+                .lines()
+                .map(|individual| {
+                    individual
+                        .chars()
+                        .map(|c| {
+                            if c.is_alphabetic() {
+                                Ok(c)
+                            } else {
+                                Err(format!("Invalid answer: {}", c))
+                            }
+                        })
+                        .collect()
+                })
+                .collect()
+        })
+        .collect()
+}
+
+fn count_individual_answers(groups: &Vec<Vec<HashSet<char>>>) -> usize {
+    groups
+        .iter()
+        .map(|group| {
+            let mut iter = group.into_iter().cloned();
+            let first = iter.next().expect("Must have at least one element");
+
+            iter.fold(first, |cumulative, entry| {
+                cumulative.intersection(&entry).copied().collect()
+            })
+            .len()
+        })
+        .sum()
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use indoc::indoc;
+
+    #[test]
+    fn test_simple() -> Result<(), Box<dyn std::error::Error>> {
+        let input = indoc!(
+            "abc
+
+             a
+             b
+             c
+
+             ab
+             ac
+
+             a
+             a
+             a
+             a
+
+             b
+            "
+        );
+
+        let groups = parse_groups(input)?;
+        let counts = count_answers(&groups);
+        assert_eq!(counts, 11);
+        Ok(())
+    }
+
+    #[test]
+    fn test_simple2() -> Result<(), Box<dyn std::error::Error>> {
+        let input = indoc!(
+            "abc
+
+             a
+             b
+             c
+
+             ab
+             ac
+
+             a
+             a
+             a
+             a
+
+             b
+            "
+        );
+
+        let groups = parse_group_individuals(input)?;
+        let counts = count_individual_answers(&groups);
+        assert_eq!(counts, 6);
+        Ok(())
+    }
+}