Days 21 and 18 part 2

1 files changed, 36 insertions, 9 deletions

diff --git a/2023/src/bin/day_18.rs b/2023/src/bin/day_18.rs
index c3e9f58..a4c9355 100644
--- a/2023/src/bin/day_18.rs
+++ b/2023/src/bin/day_18.rs
@@ -16,9 +16,11 @@ fn main() -> Result<(), Box<dyn std::error::Error>> {
     let mut fill_map = parsed.draw_map();
     fill_map.derive_inside_outside();
     dbg!(&fill_map.count_inside());
+    dbg!(&parsed.find_internal_area());
 
     let hex_parsed = Instructions::hex_parser(&input).unwrap().1;
-    dbg!(&hex_parsed);
+    dbg!(&hex_parsed.find_internal_area());
+
     Ok(())
 }
 
@@ -27,15 +29,15 @@ struct Instructions(Vec<Instruction>);
 
 #[derive(Debug)]
 struct Instruction {
-    direction: Vector2<i32>,
+    direction: Vector2<i64>,
     distance: u32,
 }
 
 #[derive(Debug)]
 struct FloodFillMap {
-    map: HashMap<Point2<i32>, Fill>,
-    top_left: Point2<i32>,
-    bottom_right: Point2<i32>,
+    map: HashMap<Point2<i64>, Fill>,
+    top_left: Point2<i64>,
+    bottom_right: Point2<i64>,
 }
 
 #[derive(Debug, PartialEq, Eq, Clone, Copy)]
@@ -71,6 +73,31 @@ impl Instructions {
 
         FloodFillMap::new(trench)
     }
+
+    fn find_internal_area(&self) -> i64 {
+        let mut current_point = Point2::new(0, 0);
+        let mut points = vec![current_point];
+
+        let mut perimeter = 0;
+        for instruction in &self.0 {
+            let next_point = current_point + instruction.direction * instruction.distance as i64;
+            points.push(next_point);
+            current_point = next_point;
+            perimeter += instruction.distance as i64;
+        }
+
+        let mut area = 0;
+        for point in points.windows(2) {
+            if let &[p1, p2] = point {
+                area += p1.x * p2.y;
+                area -= p1.y * p2.x;
+            } else {
+                unreachable!()
+            }
+        }
+
+        (perimeter + 2 + area) / 2
+    }
 }
 
 impl Instruction {
@@ -112,7 +139,7 @@ impl Instruction {
     }
 }
 
-fn dir_parser(input: &str) -> IResult<&str, Vector2<i32>> {
+fn dir_parser(input: &str) -> IResult<&str, Vector2<i64>> {
     alt((
         value(Vector2::new(0, -1), char('U')),
         value(Vector2::new(0, 1), char('D')),
@@ -121,7 +148,7 @@ fn dir_parser(input: &str) -> IResult<&str, Vector2<i32>> {
     ))(input)
 }
 
-fn hex_dir_parser(input: &str) -> IResult<&str, Vector2<i32>> {
+fn hex_dir_parser(input: &str) -> IResult<&str, Vector2<i64>> {
     alt((
         value(Vector2::new(0, -1), char('3')),
         value(Vector2::new(0, 1), char('1')),
@@ -131,7 +158,7 @@ fn hex_dir_parser(input: &str) -> IResult<&str, Vector2<i32>> {
 }
 
 impl FloodFillMap {
-    fn new(map: HashMap<Point2<i32>, Fill>) -> FloodFillMap {
+    fn new(map: HashMap<Point2<i64>, Fill>) -> FloodFillMap {
         let top_left = Point2::new(
             map.keys().map(|key| key.x).min().unwrap() - 1,
             map.keys().map(|key| key.y).min().unwrap() - 1,
@@ -166,7 +193,7 @@ impl FloodFillMap {
             .count()
     }
 
-    fn flood_fill(&mut self, start: Point2<i32>, fill: &Fill) {
+    fn flood_fill(&mut self, start: Point2<i64>, fill: &Fill) {
         let mut to_fill = vec![start];
 
         while let Some(next) = to_fill.pop() {