Add solution for 2020 day 03

2020/README.md

@@ -6,7 +6,7 @@
 | :-: | :----: | :----: | :------- |
 | 01  |   ✓    |   ✓    | Rust     |
 | 02  |   ✓    |   ✓    | Rust     |
-| 03  |        |        |          |
+| 03  |   ✓    |   ✓    | Rust     |
 | 04  |        |        |          |
 | 05  |        |        |          |
 | 06  |        |        |          |

2020/day-03/.gitignore

@@ -0,0 +1,2 @@
+part_one
+part_two

2020/day-03/common.rs

@@ -0,0 +1,64 @@
+use std::fs::File;
+use std::io::{self, Read};
+use std::path::Path;
+
+pub type Result<T> = std::result::Result<T, Box<dyn std::error::Error>>;
+
+#[derive(Debug)]
+pub struct TreeMap {
+    pub width: usize,
+    pub height: usize,
+    pub map: Vec<bool>,
+}
+
+impl TreeMap {
+    pub fn pos_has_tree(&self, x: usize, y: usize) -> bool {
+        let pos = x + (y * self.width);
+        self.map[pos]
+    }
+
+    pub fn find_in_slope(&self, dx: usize, dy: usize) -> u64 {
+        let mut tree_count = 0;
+        let mut x = 0;
+        let mut y = 0;
+
+        loop {
+            y += dy;
+
+            if y >= self.height {
+                break;
+            }
+
+            x += dx;
+            x = if x >= self.width { x - self.width } else { x };
+
+            if self.pos_has_tree(x, y) {
+                tree_count += 1;
+            };
+        }
+
+        tree_count
+    }
+}
+
+pub fn read_file<P: AsRef<Path>>(path: P) -> io::Result<TreeMap> {
+    let mut file = File::open(path)?;
+    let mut content = String::new();
+    file.read_to_string(&mut content)?;
+
+    let width = content.lines().next().unwrap().len();
+    let height = content.lines().count();
+
+    Ok(TreeMap {
+        width,
+        height,
+        map: content
+            .chars()
+            .filter_map(|ch| match ch {
+                '#' => Some(true),
+                '.' => Some(false),
+                _ => None,
+            })
+            .collect(),
+    })
+}

2020/day-03/inputs/puzzle.txt

@@ -0,0 +1,323 @@
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2020/day-03/inputs/sample.txt

@@ -0,0 +1,11 @@
+..##.......
+#...#...#..
+.#....#..#.
+..#.#...#.#
+.#...##..#.
+..#.##.....
+.#.#.#....#
+.#........#
+#.##...#...
+#...##....#
+.#..#...#.#

2020/day-03/part_one.rs

@@ -0,0 +1,16 @@
+mod common;
+
+use std::env;
+
+use common::{read_file, Result};
+
+fn main() -> Result<()> {
+    let path = env::args().skip(1).next().unwrap();
+    let map_of_trees = read_file(path)?;
+
+    let tree_count = map_of_trees.find_in_slope(3, 1);
+
+    println!("{}", tree_count);
+
+    Ok(())
+}

2020/day-03/part_two.rs

@@ -0,0 +1,19 @@
+mod common;
+
+use std::env;
+
+use common::{read_file, Result};
+
+fn main() -> Result<()> {
+    let path = env::args().skip(1).next().unwrap();
+    let map_of_trees = read_file(path)?;
+
+    let result: u64 = [(1, 1), (3, 1), (5, 1), (7, 1), (1, 2)]
+        .iter()
+        .map(|(x, y)| map_of_trees.find_in_slope(*x, *y))
+        .product();
+
+    println!("{}", result);
+
+    Ok(())
+}

README.md

@@ -7,5 +7,5 @@
 -   [2017](2017/README.md) (0% completed)
 -   [2018](2018/README.md) (0% completed)
 -   [2019](2019/README.md) (0% completed)
--   [2020](2020/README.md) (4% completed)
+-   [2020](2020/README.md) (12% completed)
 -   [2021](2021/README.md) (16% completed)