2021: day06: refacto

aoc2021/src/day06.rs

@@ -5,7 +5,7 @@ use anyhow::Result;
 
 const INPUT: &str = include_str!("../input/day06.txt");
 
-const SPAWNING_DELAY: u8 = 7;
+const SPAWNING_DELAY: usize = 7;
 const TURNS_PART_1: usize = 80;
 const TURNS_PART_2: usize = 256;
 
@@ -19,63 +19,15 @@ pub fn run() -> Result<String> {
 }
 
 fn part1(input: &str) -> Result<usize> {
-    let mut school = input
-        .trim()
-        .split(',')
-        .map(str::parse::<LanternFish>)
-        .collect::<Result<Vec<_>>>()?;
+    let mut school = input.trim().parse::<School>()?;
 
-    for _ in 0..TURNS_PART_1 {
-        let mut newly_spawned = 0;
-
-        for fish in &mut school {
-            if fish.next_turn() {
-                newly_spawned += 1;
-            }
-        }
-
-        school.resize_with(school.len() + newly_spawned, LanternFish::default)
-    }
-
-    Ok(school.len())
+    Ok(school.grow_for(TURNS_PART_1))
 }
 
 fn part2(input: &str) -> Result<usize> {
     let mut school = input.trim().parse::<School>()?;
 
-    for _ in 0..TURNS_PART_2 {
-        school.next_turn();
-    }
-
-    Ok(school.size())
-}
-
-struct LanternFish {
-    timer: u8,
-}
-
-impl LanternFish {
-    fn spawn() -> Self {
-        LanternFish {
-            timer: SPAWNING_DELAY + 1,
-        }
-    }
-
-    fn next_turn(&mut self) -> bool {
-        if self.timer == 0 {
-            self.timer = SPAWNING_DELAY - 1;
-            true
-        } else {
-            self.timer -= 1;
-            false
-        }
-    }
-}
-
-impl Default for LanternFish {
-    fn default() -> Self {
-        Self::spawn()
-    }
+    Ok(school.grow_for(TURNS_PART_2))
 }
 
 struct School {
@@ -90,38 +42,37 @@ impl School {
             self.fish_timers[i - 1] = self.fish_timers[i];
         }
 
-        self.fish_timers[SPAWNING_DELAY as usize - 1] += newly_spawned;
+        self.fish_timers[SPAWNING_DELAY - 1] += newly_spawned;
         *self.fish_timers.last_mut().unwrap() = newly_spawned;
     }
 
     fn size(&self) -> usize {
         self.fish_timers.iter().sum()
     }
+
+    fn grow_for(&mut self, turns: usize) -> usize {
+        for _ in 0..turns {
+            self.next_turn();
+        }
+
+        self.size()
+    }
 }
 
 impl std::str::FromStr for School {
     type Err = anyhow::Error;
 
     fn from_str(s: &str) -> Result<Self> {
-        let mut fish_timers = [0usize; SPAWNING_DELAY as usize + 2];
+        let mut fish_timers = [0usize; SPAWNING_DELAY + 2];
 
         for fish in s.split(',').map(str::parse::<usize>) {
-            let fish = fish?;
-            fish_timers[fish] += 1;
+            fish_timers[fish?] += 1;
         }
 
         Ok(School { fish_timers })
     }
 }
 
-impl std::str::FromStr for LanternFish {
-    type Err = anyhow::Error;
-
-    fn from_str(s: &str) -> Result<Self> {
-        Ok(LanternFish { timer: s.parse()? })
-    }
-}
-
 #[cfg(test)]
 mod tests {
     use super::*;