use view iterators (starting at tree location)

day08/common.rs

@@ -19,6 +19,20 @@ pub struct Forest {
     trees: Vec<Vec<u8>>,
 }
 
+pub enum Direction {
+    North,
+    East,
+    South,
+    West,
+}
+
+pub struct Trees<'a> {
+    forest: &'a Forest,
+    direction: Direction,
+    x: usize,
+    y: usize,
+}
+
 impl Forest {
     pub fn from_stdin() -> Result<Forest, &'static str> {
         let mut trees = vec![];
@@ -36,20 +50,30 @@ impl Forest {
     }
 
     pub fn tree(&self, x: usize, y: usize) -> Option<u8> {
-        match y < self.trees.len() && x < self.trees[0].len() {
-            false => None,
-            true => Some(self.trees[y][x]),
-        }
+        Some(*self.trees.get(y)?.get(x)?)
     }
 
-    pub fn line(&self, index: usize) -> Option<impl Iterator<Item = &u8>> {
-        Some(self.trees.get(index)?.iter())
-    }
-
-    pub fn column(&self, index: usize) -> Option<impl Iterator<Item = &u8>> {
-        match self.trees[0].len() > index {
-            false => None,
-            true => Some(self.trees.iter().map(move |line| &line[index])),
-        }
+    pub fn view(&self, x: usize, y: usize, direction: Direction) -> Option<Trees> {
+        let _ = self.tree(x, y)?;
+        Some(Trees {
+            forest: self,
+            direction: direction,
+            x: x,
+            y: y,
+        })
+    }
+}
+
+impl Iterator for Trees<'_> {
+    type Item = u8;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        match self.direction {
+            Direction::North => self.y = self.y.checked_sub(1)?,
+            Direction::East => self.x = self.x.checked_add(1)?,
+            Direction::South => self.y = self.y.checked_add(1)?,
+            Direction::West => self.x = self.x.checked_sub(1)?,
+        };
+        self.forest.tree(self.x, self.y)
     }
 }

day08/part1.rs

@@ -17,7 +17,7 @@
 
 pub mod common;
 
-use common::Forest;
+use common::{Direction, Forest};
 
 fn main() -> Result<(), &'static str> {
     let forest = Forest::from_stdin()?;
@@ -26,12 +26,16 @@ fn main() -> Result<(), &'static str> {
     for y in 0..y_len {
         for x in 0..x_len {
             let tree = forest.tree(x, y).unwrap();
-            let is_visible = forest.line(y).unwrap().take(x).all(|t| t < &tree)
-                || forest.line(y).unwrap().skip(x + 1).all(|t| t < &tree)
-                || forest.column(x).unwrap().take(y).all(|t| t < &tree)
-                || forest.column(x).unwrap().skip(y + 1).all(|t| t < &tree);
-            if is_visible {
-                result += 1;
+            for direction in [
+                Direction::North,
+                Direction::East,
+                Direction::South,
+                Direction::West,
+            ] {
+                if forest.view(x, y, direction).unwrap().all(|t| t < tree) {
+                    result += 1;
+                    break;
+                }
             }
         }
     }

day08/part2.rs

@@ -17,7 +17,7 @@
 
 pub mod common;
 
-use common::Forest;
+use common::{Direction, Forest};
 
 fn main() -> Result<(), &'static str> {
     let forest = Forest::from_stdin()?;
@@ -25,26 +25,22 @@ fn main() -> Result<(), &'static str> {
     let mut result = 0;
     for y in 0..y_len {
         for x in 0..x_len {
-            let line = forest.line(y).unwrap().collect::<Vec<_>>();
-            let column = forest.column(x).unwrap().collect::<Vec<_>>();
-
-            let west = Box::new(line[..x].iter().rev().cloned());
-            let east = Box::new(line[x + 1..].iter().cloned());
-            let north = Box::new(column[..y].iter().rev().cloned());
-            let south = Box::new(column[y + 1..].iter().cloned());
-            let views: [Box<dyn Iterator<Item = _>>; 4] = [west, east, north, south];
-
             let tree = forest.tree(x, y).unwrap();
             let mut scenic_score = 1;
-            for view in views {
+            for direction in [
+                Direction::North,
+                Direction::East,
+                Direction::South,
+                Direction::West,
+            ] {
                 let mut viewing_distance = 0;
-                for t in view {
+                for t in forest.view(x, y, direction).unwrap() {
                     match t {
-                        _ if { t >= &tree } => {
+                        _ if { t >= tree } => {
                             viewing_distance += 1;
                             break;
                         }
-                        _ if { t < &tree } => viewing_distance += 1,
+                        _ if { t < tree } => viewing_distance += 1,
                         _ => break,
                     }
                 }