Day 11. Sigh.

src/bin/ferry.rs

@@ -0,0 +1,115 @@
+use advent2020::errors::{MapOperationError, MapParseError, TopLevelError};
+use advent2020::map::Map;
+use std::convert::TryFrom;
+use std::env;
+use std::fs;
+
+#[derive(Clone, Debug, Eq, PartialEq)]
+enum FerryLocation {
+    Floor,
+    EmptySeat,
+    TakenSeat,
+}
+
+impl FerryLocation {
+    fn is_seat(&self) -> bool {
+        self != &FerryLocation::Floor
+    }
+}
+
+impl TryFrom<char> for FerryLocation {
+    type Error = MapParseError;
+
+    fn try_from(c: char) -> Result<Self,Self::Error> {
+        match c {
+            '.' => Ok(FerryLocation::Floor),
+            'L' => Ok(FerryLocation::EmptySeat),
+            '#' => Ok(FerryLocation::TakenSeat),
+            _ => Err(MapParseError::UnexpectedCharacter(c)),
+        }
+    }
+}
+
+impl Into<char> for FerryLocation {
+    fn into(self) -> char {
+        match self {
+            FerryLocation::Floor => '.',
+            FerryLocation::EmptySeat => 'L',
+            FerryLocation::TakenSeat => '#',
+        }
+    }
+}
+
+struct EvolvingMap {
+    next_map: Option<Map<FerryLocation>>,
+    occupation_tolerance: usize,
+    view: fn(&Map<FerryLocation>, usize, usize) -> Result<Vec<FerryLocation>, MapOperationError>,
+}
+
+impl From<Map<FerryLocation>> for EvolvingMap {
+    fn from(start_map: Map<FerryLocation>) -> EvolvingMap {
+        EvolvingMap {
+            next_map: Some(start_map),
+            occupation_tolerance: 4,
+            view: |m, x, y| { m.adjacents(x, y) },
+         }
+    }
+}
+
+impl Iterator for EvolvingMap {
+    type Item = Map<FerryLocation>;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        let current_map = self.next_map.clone()?;
+        let mut next_map = current_map.clone();
+
+        for (x, y, value) in current_map.locations() {
+            let occupied_neighbors = (self.view)(&current_map, x, y).ok()?.iter().filter(|x| **x == FerryLocation::TakenSeat).count();
+            match value {
+                FerryLocation::EmptySeat if occupied_neighbors == 0 => {
+                    next_map.set(x, y, FerryLocation::TakenSeat).ok()?;
+                }
+                FerryLocation::TakenSeat if occupied_neighbors >= self.occupation_tolerance => {
+                    next_map.set(x, y, FerryLocation::EmptySeat).ok()?;
+                }
+                _ => {}
+            }
+        }
+
+        if next_map == current_map {
+            self.next_map = None;
+        } else {
+            self.next_map = Some(next_map);
+        }
+
+        Some(current_map)
+    }
+}
+
+fn main() -> Result<(),TopLevelError> {
+    let filename = env::args().nth(1).expect("No file argument given.");
+    let contents = fs::read_to_string(filename)?;
+    let map = Map::<FerryLocation>::try_from(contents.as_str())?;
+
+    // part 1
+    let base_evolving_map = EvolvingMap::from(map.clone());
+    for (idx, step) in base_evolving_map.enumerate() {
+        println!("Base map, step #{}", idx);
+        step.print();
+        println!("# of occupied seats: {}\n", step.count(FerryLocation::TakenSeat));
+    }
+
+    // part 2
+    let view_evolving_map = EvolvingMap {
+        next_map: Some(map),
+        occupation_tolerance: 5,
+        view: |m,x,y| m.adjacents_until(x, y, FerryLocation::is_seat),
+    };
+    for (idx, step) in view_evolving_map.enumerate() {
+        println!("Extended map, step #{}", idx);
+        step.print();
+        println!("# of occupied seats: {}\n", step.count(FerryLocation::TakenSeat));
+    }
+
+    Ok(())
+}