From 3b877bf4cc667eb8bcc787d145203600a4dba2d2 Mon Sep 17 00:00:00 2001
From: Prefetch
Date: Sat, 25 Feb 2023 11:41:27 +0100
Subject: Initial commit

---
 d01/src/main.rs | 123 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 123 insertions(+)
 create mode 100644 d01/src/main.rs

(limited to 'd01/src')

diff --git a/d01/src/main.rs b/d01/src/main.rs
new file mode 100644
index 0000000..3117a5a
--- /dev/null
+++ b/d01/src/main.rs
@@ -0,0 +1,123 @@
+use std::fs;
+
+enum Heading {
+    North,
+    East,
+    South,
+    West,
+}
+
+impl Heading {
+    fn turn_left(&mut self) {
+        *self = match *self {
+            Heading::North => Heading::West,
+            Heading::East  => Heading::North,
+            Heading::South => Heading::East,
+            Heading::West  => Heading::South,
+        };
+    }
+
+    fn turn_right(&mut self) {
+        *self = match *self {
+            Heading::North => Heading::East,
+            Heading::East  => Heading::South,
+            Heading::South => Heading::West,
+            Heading::West  => Heading::North,
+        };
+    }
+}
+
+fn get_route(input: &str) -> Vec<(isize, isize)> {
+    let steps: Vec<&str> = input.trim().split(", ").collect();
+
+    let mut pos = (0, 0);
+    let mut route = vec![pos];
+
+    let mut facing = Heading::North;
+    for s in steps {
+        // Read which way to turn
+        if s.starts_with("L") {
+            facing.turn_left();
+        } else if s.starts_with("R") {
+            facing.turn_right();
+        }
+
+        // Read how far to go in the new direction
+        let dist: usize = s[1..].parse().unwrap();
+
+        // Add each 1-block step to `route' so that part 2 can be solved
+        for _i in 0..dist {
+            pos = match facing {
+                Heading::North => (pos.0 + 1, pos.1),
+                Heading::East  => (pos.0, pos.1 + 1),
+                Heading::South => (pos.0 - 1, pos.1),
+                Heading::West  => (pos.0, pos.1 - 1),
+            };
+            route.push(pos);
+        }
+    }
+
+    route
+}
+
+fn solve_part1(input: &str) -> isize {
+    let route = get_route(input);
+    let ended = route.last().unwrap();
+
+    // Manhattan distance from origin to `ended' position
+    ended.0.abs() + ended.1.abs()
+}
+
+fn solve_part2(input: &str) -> Option<isize> {
+    let route = get_route(input);
+
+    for i in 1..route.len() {
+        let pos = route[i - 1];
+        if route[i..].contains(&pos) {
+            // Manhattan distance to first twice-visited position
+            return Some(pos.0.abs() + pos.1.abs());
+        }
+    }
+
+    None
+}
+
+fn main() {
+    // Read instructions from input text file
+    let input = fs::read_to_string("input.txt").unwrap();
+
+    // Part 1 gives 181 for me
+    println!("Part 1 solution: {}", solve_part1(&input));
+
+    // Part 2 gives 140 for me
+    println!("Part 2 solution: {}", solve_part2(&input).unwrap());
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn part1_example1() {
+        let input = "R2, L3";
+        assert_eq!(solve_part1(input), 5);
+    }
+
+    #[test]
+    fn part1_example2() {
+        let input = "R2, R2, R2";
+        assert_eq!(solve_part1(input), 2);
+    }
+
+    #[test]
+    fn part1_example3() {
+        let input = "R5, L5, R5, R3";
+        assert_eq!(solve_part1(input), 12);
+    }
+
+    #[test]
+    fn part2_example1() {
+        let input = "R8, R4, R4, R8";
+        assert_eq!(solve_part2(input).unwrap(), 4);
+    }
+}
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