From a09a82c05d5ee25ceed5491c98503c030eabe406 Mon Sep 17 00:00:00 2001
From: Alpha Chen <alpha.chen@gmail.com>
Date: Wed, 12 Dec 2018 22:26:00 -0800
Subject: [PATCH] [2018][rust][12.1]

---
 2018/rust/src/bin/day_12.rs | 161 ++++++++++++++++++++++++++++++++++++
 1 file changed, 161 insertions(+)
 create mode 100644 2018/rust/src/bin/day_12.rs

diff --git a/2018/rust/src/bin/day_12.rs b/2018/rust/src/bin/day_12.rs
new file mode 100644
index 0000000..960c8a9
--- /dev/null
+++ b/2018/rust/src/bin/day_12.rs
@@ -0,0 +1,161 @@
+use std::collections::HashMap;
+use std::error::Error;
+use std::fmt;
+use std::str::FromStr;
+
+use regex::Regex;
+
+use advent_of_code::main;
+
+main!();
+
+fn solve(input: &str) -> Result<String, Box<Error>> {
+    let mut generation: Generation = input.parse()?;
+    for _ in 0..19 {
+        generation.next();
+    }
+
+    let pots = generation.next().unwrap();
+    let indices: Vec<_> = pots.iter().filter(|(_,&v)| v).map(|(&k,_)| k).collect();
+    let output: isize = indices.iter().sum();
+
+    Ok(output.to_string())
+}
+
+#[test]
+fn test_solve() {
+    let input = r"
+initial state: #..#.#..##......###...###
+
+...## => #
+..#.. => #
+.#... => #
+.#.#. => #
+.#.## => #
+.##.. => #
+.#### => #
+#.#.# => #
+#.### => #
+##.#. => #
+##.## => #
+###.. => #
+###.# => #
+####. => #
+    ";
+
+    assert_eq!(solve(&input).unwrap(), 325.to_string());
+}
+
+struct Generation {
+    pots: HashMap<isize, bool>,
+    notes: HashMap<String, bool>,
+}
+
+impl fmt::Display for Generation {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        let plants: Vec<_> = self
+            .pots
+            .iter()
+            .filter(|(_, &v)| v)
+            .map(|(&k, _)| k)
+            .collect();
+        let min = *plants.iter().min().unwrap();
+        let max = *plants.iter().max().unwrap();
+        let s: String = (min..=max)
+            .map(|x| self.pots.get(&x).unwrap_or_else(|| &false))
+            .map(|&x| if x { '#' } else { '.' })
+            .collect();
+        write!(f, "{}", s)
+    }
+}
+
+impl Iterator for Generation {
+    type Item = HashMap<isize, bool>;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        let plants: Vec<_> = self
+            .pots
+            .iter()
+            .filter(|(_, &v)| v)
+            .map(|(&k, _)| k)
+            .collect();
+        let min = *plants.iter().min().unwrap() - 2;
+        let max = *plants.iter().max().unwrap() + 2;
+        self.pots = (min..=max)
+            .map(|i| {
+                let key: String = ((i - 2)..=(i + 2))
+                    .map(|x| self.pots.get(&x).unwrap_or_else(|| &false))
+                    .map(|&x| if x { '#' } else { '.' })
+                    .collect();
+                let value = *self.notes.get(&key).unwrap_or_else(|| &false);
+                (i, value)
+            })
+            .collect();
+
+        Some(self.pots.clone())
+    }
+}
+
+#[test]
+fn test_generation() {
+    let input = r"
+initial state: #..#.#..##......###...###
+
+...## => #
+..#.. => #
+.#... => #
+.#.#. => #
+.#.## => #
+.##.. => #
+.#### => #
+#.#.# => #
+#.### => #
+##.#. => #
+##.## => #
+###.. => #
+###.# => #
+####. => #
+    ";
+    let mut generation: Generation = input.parse().unwrap();
+    let pots = generation.pots.clone();
+    assert!(pots.get(&0).unwrap());
+    assert!(pots.get(&3).unwrap());
+    assert!(!pots.get(&4).unwrap());
+
+    let pots = generation.next().unwrap();
+    assert!(pots.get(&0).unwrap());
+    assert!(!pots.get(&3).unwrap());
+    assert!(pots.get(&4).unwrap());
+}
+
+impl FromStr for Generation {
+    type Err = Box<Error>;
+
+    fn from_str(s: &str) -> Result<Self, Self::Err> {
+        let mut lines = s.trim().lines();
+
+        let initial_state = lines.next().unwrap();
+        let pots = Regex::new(r"[.#]+")
+            .ok()
+            .and_then(|re| re.find(initial_state))
+            .unwrap()
+            .as_str()
+            .chars()
+            .enumerate()
+            .map(|(i, c)| (i as isize, c == '#'))
+            .collect();
+
+        lines.next(); // skip blank line
+
+        let notes = lines
+            .map(|line| {
+                let mut note = line.split(" => ");
+                let key = note.next().unwrap();
+                let value = note.next().unwrap() == "#";
+                (key.into(), value)
+            })
+            .collect();
+
+        Ok(Generation { pots, notes })
+    }
+}