Add 2020 - Day 3 - Part 2

2020/03/main.rs

@@ -2,8 +2,6 @@ use std::error::Error;
 
 use grid::{Grid, GridLine};
 
-use crate::grid::Cell;
-
 #[path = "../utils/mod.rs"]
 mod utils;
 
@@ -11,24 +9,22 @@ fn main() -> Result<(), Box<dyn Error>> {
 	let lines = utils::parse_input_lines::<GridLine>()?;
 	let grid = Grid::from(lines)?;
 	
-	let mut x = 0;
-	let mut y = 0;
-	let mut trees = 0;
+	println!("Total trees on slope going 3 right 1 down: {}", grid.count_trees_on_slope(3, 1));
 	
-	loop {
-		match grid.get_at(x, y) {
-			None => break,
-			Some(Cell::Open) => {}
-			Some(Cell::Tree) => {
-				trees += 1;
-			}
-		}
-		
-		x += 3;
-		y += 1;
+	let mut product = 1u32;
+	let slopes = vec![
+		(1, 1),
+		(3, 1),
+		(5, 1),
+		(7, 1),
+		(1, 2)
+	];
+	
+	for (down, right) in slopes {
+		product *= grid.count_trees_on_slope(down, right);
 	}
 	
-	println!("Total trees: {}", trees);
+	println!("Product of all attempted slopes: {}", product);
 	
 	Ok(())
 }
@@ -58,6 +54,27 @@ mod grid {
 			let line = self.data.get(y as usize)?;
 			Some(line.get_at(x))
 		}
+		
+		pub fn count_trees_on_slope(&self, step_x: i32, step_y: i32) -> u32 {
+			let mut x = 0;
+			let mut y = 0;
+			let mut trees = 0u32;
+			
+			loop {
+				match self.get_at(x, y) {
+					None => break,
+					Some(Cell::Open) => {}
+					Some(Cell::Tree) => {
+						trees += 1;
+					}
+				}
+				
+				x += step_x;
+				y += step_y;
+			}
+			
+			return trees;
+		}
 	}
 	
 	pub struct GridLine {