Day 9. Pretty straight forward. The borrow checker must have felt bad for me and did not give me any problems today

day9/Cargo.lock

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+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+version = 3
+
+[[package]]
+name = "day9"
+version = "0.1.0"

day9/Cargo.toml

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+[package]
+name = "day9"
+version = "0.1.0"
+edition = "2021"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]

day9/src/main.rs

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+use std::collections::HashMap;
+
+fn main() {
+    let contents = std::fs::read_to_string("data.txt").expect("Failed to read file");
+    let lines = contents.lines().collect::<Vec<&str>>();
+
+    let mut hash: HashMap<(i32, i32), bool> = HashMap::new();
+    run(&lines, &mut hash, 1);
+    let part_1 = hash.keys().len();
+    println!("Num visited, part 1: {:?}", part_1);
+
+    let mut hash2: HashMap<(i32, i32), bool> = HashMap::new();
+    run(&lines, &mut hash2, 9);
+    let part_2 = hash2.keys().len();
+    println!("Num visited, part 2: {:?}", part_2);
+}
+
+fn run(lines: &Vec<&str>, hash: &mut HashMap<(i32, i32), bool>, num_tails: usize) {
+    let mut head = (0i32, 0i32);
+    let mut tails: Vec<(i32, i32)> = vec![(0, 0); num_tails];
+
+    for line in lines {
+        let (dir, steps) = line.split_once(" ").unwrap();
+
+        for _ in 0..steps.parse().unwrap() {
+            match dir {
+                "L" => head = (head.0, head.1 - 1),
+                "R" => head = (head.0, head.1 + 1),
+                "U" => head = (head.0 - 1, head.1),
+                "D" => head = (head.0 + 1, head.1),
+                _ => (),
+            }
+            // println!("\nnew head location {:?}", head);
+
+            let mut parent = head;
+
+            for tail_i in 0..num_tails {
+                let mut tail = tails[tail_i];
+
+                // find the distance from parent to tail
+                let v_dist = parent.0 - tail.0;
+                let h_dist = parent.1 - tail.1;
+                let mut already_moved_diagonally = false;
+
+                // move vertically
+                if v_dist.abs() > 1 {
+                    let v_diff = v_dist / v_dist.abs();
+                    tail = (tail.0 + v_diff, tail.1);
+
+                    // do we need to move horizontally?
+                    if parent.1 != tail.1 {
+                        let h_diff = h_dist / h_dist.abs();
+                        tail = (tail.0, tail.1 + h_diff);
+                        already_moved_diagonally = true;
+                    }
+                }
+
+                // move horizontally
+                if h_dist.abs() > 1 && !already_moved_diagonally {
+                    let h_diff = h_dist / h_dist.abs();
+                    tail = (tail.0, tail.1 + h_diff);
+
+                    // do we need to move horizontally?
+                    if parent.0 != tail.0 {
+                        let v_diff = v_dist / v_dist.abs();
+                        tail = (tail.0 + v_diff, tail.1);
+                    }
+                }
+
+                // println!("new tail ({:?}) location {:?}", tail_i + 1, tail);
+                if tail_i == num_tails - 1 {
+                    // for the last tail, record where it has been
+                    hash.insert(tail, true);
+                }
+
+                tails[tail_i] = tail;
+                parent = tail;
+            }
+        }
+
+        let mut temp = tails.to_owned();
+        temp.insert(0, head);
+        display(temp);
+    }
+}
+
+fn display(rope: Vec<(i32, i32)>) -> () {
+    let v_min = rope.iter().map(|x| x.0).min().unwrap();
+    let v_max = rope.iter().map(|x| x.0).max().unwrap();
+    let h_min = rope.iter().map(|x| x.1).min().unwrap();
+    let h_max = rope.iter().map(|x| x.1).max().unwrap();
+
+    for v in v_min..=v_max {
+        for h in h_min..=h_max {
+            match rope.iter().position(|&x| x == (v, h)) {
+                Some(i) => print!("{i}"),
+                None => print!("."),
+            }
+        }
+        println!("");
+    }
+    println!("");
+}

day9/test.txt

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+R 4
+U 4
+L 3
+D 1
+R 4
+D 1
+L 5
+R 2

day9/test2.txt

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+R 5
+U 8
+L 8
+D 3
+R 17
+D 10
+L 25
+U 20