Day 3

src/day3.rs

@@ -0,0 +1,54 @@
+use aoc_runner_derive::{aoc,aoc_generator};
+pub struct Forest {
+    slice: Vec<Vec<bool>>,
+}
+
+impl Forest {
+    fn get(&self, x: usize,y: usize) -> Option<bool> {
+        self.slice.get(y).map(|line| line.get(x%line.len())).flatten().cloned()
+    }
+}
+
+
+#[aoc_generator(day3)]
+pub fn input_generator(input: &str) -> Forest {
+    let slice=input.lines().map(|l| l.chars().map(|c| c=='#').collect()).collect();
+    Forest{
+        slice
+    }
+}
+
+#[aoc(day3,part1)]
+pub fn solve_part1(input: &Forest) -> usize {
+    let mut sum: usize=0;
+    let dx=3;
+    let dy=1;
+    let mut pos=(0,0);
+    while let Some(tree) = input.get(pos.0,pos.1) {
+        if tree {
+            sum+=1;
+        }
+        pos.0+=dx;
+        pos.1+=dy;
+    };
+    sum
+}
+
+
+#[aoc(day3,part2)]
+pub fn solve_part2(input: &Forest) -> usize {
+    let mut prod: usize = 1;
+    for (dx,dy) in &[(1,1),(3,1),(5,1),(7,1),(1,2)] {
+        let mut sum: usize=0;
+        let mut pos=(0,0);
+        while let Some(tree) = input.get(pos.0,pos.1) {
+            if tree {
+                sum+=1;
+            }
+            pos.0+=dx;
+            pos.1+=dy;
+        };
+        prod*=sum;
+    }
+    prod
+}

src/lib.rs

@@ -1,4 +1,5 @@
 use aoc_runner_derive::aoc_lib;
 pub mod day1;
 pub mod day2;
+pub mod day3;
 aoc_lib! { year = 2020 }