2020: day03: part 1

aoc2020/src/day03.rs

@@ -0,0 +1,119 @@
+use std::fmt::Write;
+use std::iter::FromIterator;
+use std::ops::Index;
+use std::str::FromStr;
+
+const INPUT: &str = include_str!("../input/day03.txt");
+
+pub fn run() -> aoc::Result<String> {
+    let mut res = String::with_capacity(128);
+
+    writeln!(res, "part 1: {}", part1(INPUT)?)?;
+
+    Ok(res)
+}
+
+fn part1(input: &str) -> aoc::Result<u64> {
+    let forest = input.parse()?;
+
+    Ok(count_trees(forest))
+}
+
+fn count_trees(forest: Forest) -> u64 {
+    let mut count = 0;
+
+    let vertical_range = 0..forest.height();
+    let horizontal_range = (0..).step_by(3);
+
+    for (i, j) in vertical_range.zip(horizontal_range) {
+        if forest[i][j] {
+            count += 1
+        }
+    }
+
+    count
+}
+
+#[derive(Debug)]
+struct ForestLine {
+    trees: Vec<bool>,
+}
+
+impl Index<usize> for ForestLine {
+    type Output = bool;
+
+    fn index(&self, i: usize) -> &Self::Output {
+        &self.trees[i % self.trees.len()]
+    }
+}
+
+impl FromIterator<bool> for ForestLine {
+    fn from_iter<I>(iter: I) -> Self
+    where
+        I: IntoIterator<Item = bool>,
+    {
+        Self {
+            trees: iter.into_iter().collect(),
+        }
+    }
+}
+
+#[derive(Debug)]
+struct Forest {
+    trees: Vec<ForestLine>,
+}
+
+impl Forest {
+    fn height(&self) -> usize {
+        self.trees.len()
+    }
+}
+
+impl Index<usize> for Forest {
+    type Output = ForestLine;
+
+    fn index(&self, i: usize) -> &Self::Output {
+        if i >= self.height() {
+            panic!("forest is of size {}, tried to access {}", self.height(), i);
+        }
+
+        &self.trees[i]
+    }
+}
+
+impl FromStr for Forest {
+    type Err = aoc::Error;
+
+    fn from_str(s: &str) -> aoc::Result<Self> {
+        let trees = s
+            .lines()
+            .map(|line| {
+                line.chars()
+                    .map(|c| match c {
+                        '.' => false,
+                        _ => true,
+                    })
+                    .collect()
+            })
+            .collect();
+
+        Ok(Self { trees })
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    static PROVIDED: &'static str = include_str!("../input/day03_provided.txt");
+
+    #[test]
+    fn part1_provided() {
+        assert_eq!(part1(PROVIDED).unwrap(), 7);
+    }
+
+    #[test]
+    fn part1_real() {
+        assert_eq!(part1(INPUT).unwrap(), 242);
+    }
+}

aoc2020/src/lib.rs

@@ -1,2 +1,3 @@
 pub mod day01;
 pub mod day02;
+pub mod day03;

aoc2020/src/main.rs

@@ -3,9 +3,10 @@ use aoc::Result;
 
 use aoc2020::day01;
 use aoc2020::day02;
+use aoc2020::day03;
 
 fn main() -> Result<()> {
-    let days: &[DayFunc] = &[day01::run, day02::run];
+    let days: &[DayFunc] = &[day01::run, day02::run, day03::run];
 
     aoc::run(days)
 }