Add 2016 day 1

.gitignore

@@ -2,4 +2,5 @@ node_modules/
 *.hi
 *.o
 *.exe
+target/
 input.txt

2016/Cargo.toml

@@ -0,0 +1,6 @@
+[package]
+name = "aoc2016"
+version = "0.1.0"
+edition = "2021"
+
+[dependencies]

2016/src/bin/day1.rs

@@ -0,0 +1,89 @@
+use std::fs::File;
+use std::io::prelude::*;
+use std::path::Path;
+use std::collections::HashSet;
+
+#[derive(PartialEq, Clone, Copy)]
+enum Direction {
+    North,
+    East,
+    South,
+    West
+}
+
+fn turn(dir: &str, curr: &Direction) -> Direction {
+    let dirs = [Direction::North, Direction::East, Direction::South, Direction::West];
+    let index = dirs.iter().position(|s| s == curr).unwrap();
+
+    match dir {
+        "R" => { dirs[(index + 1) % 4] }
+        "L" => { dirs[(4 + index - 1) % 4] },
+        _ => panic!("Tried to turn unknown direction {}", dir)
+    }
+}
+
+fn move_dist(loc: (i32, i32), dir: &Direction, dist: i32, visited: &mut HashSet<(i32, i32)>) -> ((i32, i32), Option<(i32, i32)>) {
+    let (x, y) = loc;
+
+    let (new_x, new_y) = match *dir {
+        Direction::North => { (x, y + dist) },
+        Direction::East  => { (x + dist, y) },
+        Direction::South => { (x, y - dist) },
+        Direction::West  => { (x - dist, y) }
+    };
+
+    let mut already_visited = None;
+
+    for i in 1..dist {
+        let curr = (x + ((new_x - x) / dist) * i, y + ((new_y - y) / dist) * i);
+
+        if visited.contains(&curr) && already_visited.is_none() {
+            already_visited = Some(curr);
+        }
+        else {
+            visited.insert(curr);
+        }
+    }
+
+    ((new_x, new_y), already_visited)
+}
+
+fn manhattan_dist(loc: (i32, i32)) -> i32 {
+    return loc.0.abs() + loc.1.abs();
+}
+
+fn main() {
+    let path = Path::new("input.txt");
+    let display = path.display();
+
+    let mut file = match File::open(&path) {
+        Err(why) => panic!("couldn't open {}: {}", display, why),
+        Ok(file) => file,
+    };
+
+    let mut s = String::new();
+    file.read_to_string(&mut s).unwrap();
+
+    let parts = s.trim().split(", ");
+
+    let mut loc = (0, 0);
+    let mut dir = Direction::North;
+    let mut visited = HashSet::new();
+    let mut already_visited = None;
+
+    for p in parts {
+        let (first, rest) = p.split_at(1);
+        let distance = rest.parse::<i32>().unwrap();
+
+        dir = turn(first, &dir);
+        let result = move_dist(loc, &dir, distance, &mut visited);
+        loc = result.0;
+
+        if already_visited.is_none() && result.1.is_some() {
+            already_visited = result.1;
+        }
+    }
+
+    println!("part 1 {}", manhattan_dist(loc));
+    println!("part 2 {}", manhattan_dist(already_visited.unwrap()));
+}