day 9 :3

Cargo.lock

@@ -34,6 +34,10 @@ version = "0.1.0"
 name = "day08"
 version = "0.1.0"
 
+[[package]]
+name = "day09"
+version = "0.1.0"
+
 [[package]]
 name = "tiesto"
 version = "0.1.0"

Cargo.toml

@@ -10,7 +10,7 @@ members = [
 	"day06",
 	"day07",
 	"day08",
-#	"day09",
+	"day09",
 #	"day10",
 #	"day11",
 #	"day12",

day09/Cargo.toml

@@ -0,0 +1,8 @@
+[package]
+name = "day09"
+version = "0.1.0"
+edition = "2021"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]

day09/src/main.rs

@@ -0,0 +1,91 @@
+use std::fs;
+use std::iter;
+use std::str::FromStr;
+use std::collections::HashSet;
+
+fn main() {
+    const FILE_PATH: &str = "input";
+    println!("Hi this is the nineth day of AOC2022, first we will read the file {}", FILE_PATH);
+    let contents = fs::read_to_string(FILE_PATH)
+        .expect("Should have been able to read the file");
+
+    println!("The ammount of visited positions are: {}", get_positions(&contents, 1).len());
+    println!("The ammount of visited positions are: {}", get_positions(&contents, 9).len());
+}
+
+fn get_positions(input: &str, num_knots: usize) -> HashSet<(i32, i32)> {
+    let moves: Vec<_> = input.lines().map(|l| {
+        let l: Vec<_> = l.split(" ").collect();
+        let dir = match &l[0] {
+            &"U" => (0, 1),
+            &"D" => (0, -1),
+            &"L" => (-1, 0),
+            &"R" => (1, 0),
+            &_ => unreachable!()
+        };
+        iter::repeat(dir).take(usize::from_str(l[1]).expect("NaN"))
+    }).flatten().collect();
+    let mut head = (0,0);
+    let mut knots = vec![(0,0); num_knots];
+    let mut visited = HashSet::new();
+
+    for m in moves {
+        head = (head.0+m.0, head.1+m.1);
+        knots[0] = move_tail(head, knots[0]);
+        for i in 1..num_knots {
+            knots[i] = move_tail(knots[i-1], knots[i]);
+        }
+        visited.insert(knots[num_knots-1]);
+    }
+
+    visited
+}
+
+fn move_tail(head: (i32, i32), tail: (i32, i32)) -> (i32, i32) {
+    let dx = head.0 - tail.0;
+    let dy = head.1 - tail.1;
+
+    if dx.abs() <= 1 && dy.abs() <= 1 {return tail;}
+
+    match (dx, dy) {
+        (2,2) => (tail.0+1, tail.1+1),
+        (-2,2) => (tail.0-1, tail.1+1),
+        (2,-2) => (tail.0+1, tail.1-1),
+        (-2,-2) => (tail.0-1, tail.1-1),
+        (2,y) => (tail.0+1, tail.1+y),
+        (-2,y) => (tail.0-1, tail.1+y),
+        (x,2) => (tail.0+x, tail.1+1),
+        (x,-2) => (tail.0+x, tail.1-1),
+        _ => unreachable!()
+    }
+
+}
+
+#[cfg(test)]
+mod test {
+    const INPUT: &str = r#"R 4
+U 4
+L 3
+D 1
+R 4
+D 1
+L 5
+R 2"#;
+    const INPUT2: &str = r#"R 5
+U 8
+L 8
+D 3
+R 17
+D 10
+L 25
+U 20"#;
+    use super::*;
+    #[test]
+    fn rope1() {
+        assert_eq!(get_positions(INPUT, 1).len(), 13);
+    }
+    #[test]
+    fn rope2() {
+        assert_eq!(get_positions(INPUT2, 9).len(), 36);
+    }
+}