diff --git a/src/bin/day08.rs b/src/bin/day08.rs
index deeab84..5e6c131 100644
--- a/src/bin/day08.rs
+++ b/src/bin/day08.rs
@@ -10,45 +10,49 @@ use tracing_subscriber::EnvFilter;
 type Input = Vec<Vec<i8>>;
 type Output = usize;
 
+type SignedPosition = Vector2D<isize>;
 type Position = Vector2D<usize>;
 type Visited = BTreeSet<Position>;
 
-fn count_in(trees: &Input, counted: &mut BTreeSet<(usize, usize)>, swap: bool) {
+fn count_in(trees: &Input, counted: &mut Visited, swap: bool) {
     fn folder(
         trees: &Input,
-        counted: &mut BTreeSet<(usize, usize)>,
-        mut x: usize,
-        mut y: usize,
+        counted: &mut Visited,
+        mut pos: Position,
         swap: bool,
         tallest: i8,
     ) -> i8 {
         if swap {
-            (x, y) = (y, x);
+            pos = pos.swap();
         }
 
-        if trees[y][x] > tallest {
-            counted.insert((x, y));
+        if *index(trees, &pos) > tallest {
+            counted.insert(pos);
         }
 
-        max(tallest, trees[y][x])
+        max(tallest, *index(trees, &pos))
     }
 
     (0..trees.len()).for_each(|y| {
-        (0..trees[y].len()).fold(-1, |tallest, x| folder(trees, counted, x, y, swap, tallest));
-        (0..trees[y].len()).rfold(-1, |tallest, x| folder(trees, counted, x, y, swap, tallest));
+        (0..trees[y].len()).fold(-1, |tallest, x| {
+            folder(trees, counted, Position::new(x, y), swap, tallest)
+        });
+        (0..trees[y].len()).rfold(-1, |tallest, x| {
+            folder(trees, counted, Position::new(x, y), swap, tallest)
+        });
     })
 }
 
-fn count_in_rows(trees: &Input, counted: &mut BTreeSet<(usize, usize)>) {
+fn count_in_rows(trees: &Input, counted: &mut Visited) {
     count_in(trees, counted, false)
 }
 
-fn count_in_columns(trees: &Input, counted: &mut BTreeSet<(usize, usize)>) {
+fn count_in_columns(trees: &Input, counted: &mut Visited) {
     count_in(trees, counted, true)
 }
 
 fn part_1(input: &Input) -> Output {
-    let mut counted: BTreeSet<(usize, usize)> = BTreeSet::new();
+    let mut counted = Visited::new();
 
     count_in_rows(input, &mut counted);
     count_in_columns(input, &mut counted);
@@ -56,20 +60,15 @@ fn part_1(input: &Input) -> Output {
     counted.len()
 }
 
-fn in_range(trees: &Input, x: i32, y: i32) -> bool {
-    y >= 0 && y < trees.len() as i32 && x >= 0 && x < trees[y as usize].len() as i32
-}
-
-fn count_visible(trees: &Input, x: i32, y: i32, dx: i32, dy: i32) -> usize {
-    let max_height = trees[y as usize][x as usize];
-    let mut d = 1;
-
+fn count_visible(trees: &Input, position: SignedPosition, diff: SignedPosition) -> usize {
+    let max_height = *index(trees, &position);
     let mut visible = 0;
 
-    while in_range(trees, x + d * dx, y + d * dy) {
+    let mut d = 1;
+    while in_range(trees, &(position + diff * d)) {
         visible += 1;
 
-        if trees[(y + d * dy) as usize][(x + d * dx) as usize] >= max_height {
+        if *index(trees, &(position + diff * d)) >= max_height {
             break;
         }
 
@@ -79,17 +78,23 @@ fn count_visible(trees: &Input, x: i32, y: i32, dx: i32, dy: i32) -> usize {
     visible as usize
 }
 
-fn compute_scenic_score(trees: &Input, x: i32, y: i32) -> usize {
+fn compute_scenic_score(trees: &Input, x: isize, y: isize) -> usize {
     vec![(0, 1), (1, 0), (0, -1), (-1, 0)]
         .iter()
-        .map(|&(dx, dy)| count_visible(trees, x, y, dx, dy))
+        .map(|&(dx, dy)| {
+            count_visible(
+                trees,
+                SignedPosition::new(x, y),
+                SignedPosition::new(dx, dy),
+            )
+        })
         .product()
 }
 
 fn part_2(input: &Input) -> Output {
     (0..input.len())
         .flat_map(|y| {
-            (0..input[y].len()).map(move |x| compute_scenic_score(input, x as i32, y as i32))
+            (0..input[y].len()).map(move |x| compute_scenic_score(input, x as isize, y as isize))
         })
         .max()
         .unwrap()