2017/12.

2017/12/Cargo.lock

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+[[package]]
+name = "day-12"
+version = "0.1.0"
+

2017/12/Cargo.toml

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+[package]
+name = "day-12"
+version = "0.1.0"
+authors = ["logaritmisk <anders.e.olsson@gmail.com>"]
+
+[dependencies]

2017/12/src/main.rs

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+use std::io::{self, Read};
+use std::collections::{HashMap, HashSet};
+
+
+fn parse(input: &str) -> (usize, Vec<usize>) {
+    let parts = input.split("<->").collect::<Vec<_>>();
+
+    let from = parts[0].trim().parse::<usize>()
+        .expect("faild to parse from");
+
+    let to = parts[1].split(',').filter_map(|to| to.trim().parse::<usize>().ok()).collect::<Vec<_>>();
+
+    (from, to)
+}
+
+fn main() {
+    let mut input = String::new();
+
+    io::stdin().read_to_string(&mut input)
+        .expect("faild to read input");
+
+    let pipes = input.lines().filter(|line| !line.is_empty()).map(parse).collect::<Vec<_>>();
+
+    let mut groups = HashMap::new();
+
+    groups.entry(0).or_insert_with(HashSet::new).insert(0);
+
+    loop {
+        let mut done = true;
+
+        pipes.iter().for_each(|&(from, ref to)| {
+            let mut create = true;
+
+            for group in groups.values_mut() {
+                if group.contains(&from) {
+                    create = false;
+
+                    for id in to {
+                        if group.insert(*id) {
+                            done = false;
+                        }
+                    }
+                }
+            }
+
+            if create {
+                let group = groups.entry(from).or_insert_with(HashSet::new);
+
+                group.insert(from);
+
+                for id in to {
+                    group.insert(*id);
+                }
+            }
+        });
+
+        if done {
+            break;
+        }
+    }
+
+    println!("part_one={}", groups[&0].len());
+    println!("part_two={}", groups.len());
+}
+
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+
+    #[test]
+    fn test_parse() {
+        assert_eq!(parse("0 <-> 2"), (0, vec![2]));
+        assert_eq!(parse("1 <-> 1"), (1, vec![1]));
+        assert_eq!(parse("2 <-> 0, 3, 4"), (2, vec![0, 3, 4]));
+    }
+}