Day 20, part 2

src/bin/d20p1.rs

@@ -0,0 +1,9 @@
+use aoc22::{day20, util};
+
+pub fn main() {
+    let nodes = day20::parse_file(&util::parse_input(), 1);
+
+    day20::mix(&nodes);
+
+    println!("Sum of coordinates: {}", day20::calc_coordinates(&nodes));
+}

src/bin/d20p2.rs

@@ -0,0 +1,16 @@
+use aoc22::{day20, util};
+
+const KEY: isize = 811589153;
+const ROUNDS: usize = 10;
+
+pub fn main() {
+    let nodes = day20::parse_file(&util::parse_input(), KEY);
+    // day20::print_nodes(&nodes);
+
+    for _ in 0..ROUNDS {
+        day20::mix(&nodes);
+        // day20::print_nodes(&nodes);
+    }
+
+    println!("Sum of coordinates: {}", day20::calc_coordinates(&nodes));
+}

src/day20.rs

@@ -0,0 +1,122 @@
+use std::{cell::RefCell, fmt::Debug, ops::Deref, rc::Rc};
+
+pub struct Node {
+    pub val: isize,
+    pub next: Option<Rc<RefCell<Node>>>,
+    pub prev: Option<Rc<RefCell<Node>>>,
+}
+
+// Default Debug implementation will loop indefinitely, since we have a ring buffer
+impl Debug for Node {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        f.debug_struct("Node")
+            .field("val", &self.val)
+            .field("next", &self.next.as_ref().map(|n| n.borrow().val))
+            .field("prev", &self.prev.as_ref().map(|n| n.borrow().val))
+            .finish()
+    }
+}
+
+pub fn get_next(node: &Rc<RefCell<Node>>, n: usize) -> Rc<RefCell<Node>> {
+    let mut curr = node.clone();
+    for _ in 0..n {
+        let next = curr.borrow().next.as_ref().unwrap().clone();
+        curr = next;
+    }
+    curr
+}
+
+pub fn get_prev(node: &Rc<RefCell<Node>>, n: usize) -> Rc<RefCell<Node>> {
+    let mut curr = node.clone();
+    for _ in 0..n {
+        let prev = curr.borrow().prev.as_ref().unwrap().clone();
+        curr = prev;
+    }
+    curr
+}
+
+pub fn parse_file(input: &String, key: isize) -> Vec<Rc<RefCell<Node>>> {
+    let mut result = Vec::new();
+
+    let mut last = None;
+    for line in input.lines() {
+        let val: isize = line.parse().unwrap();
+        let node = Rc::new(RefCell::new(Node {
+            val: val * key,
+            next: None,
+            prev: last.clone(),
+        }));
+        if let Some(l) = last {
+            l.as_ref().borrow_mut().next = Some(node.clone());
+        }
+        result.push(node.clone());
+        last = Some(node);
+    }
+
+    assert!(result.len() > 0);
+
+    let last_refcell = last.as_ref().unwrap().deref();
+    last_refcell.borrow_mut().next = Some(result[0].clone());
+    let first_refcell = &*result[0];
+    first_refcell.borrow_mut().prev = Some(last.as_ref().unwrap().clone());
+
+    result
+}
+
+pub fn mix(nodes: &Vec<Rc<RefCell<Node>>>) {
+    let div = nodes.len() - 1;
+
+    for node in nodes {
+        let n = node.borrow().val;
+        if n == 0 || (n > 0 && (n as usize) % div == 0) || (n < 0 && (-n as usize) % div == 0) {
+            continue;
+        }
+
+        // Remove from current position
+        let prev = get_prev(node, 1);
+        let next = get_next(node, 1);
+        prev.borrow_mut().next = Some(next.clone());
+        next.borrow_mut().prev = Some(prev.clone());
+
+        let prev = if n > 0 {
+            let n = (n as usize) % div;
+            assert!(n < div);
+            get_next(node, n)
+        } else {
+            let n = ((-n as usize) % div) + 1;
+            assert!(n < div);
+            get_prev(node, n)
+        };
+        let next = get_next(&prev, 1);
+        prev.deref().borrow_mut().next = Some(node.clone());
+        next.deref().borrow_mut().prev = Some(node.clone());
+
+        let mut n_mut = node.deref().borrow_mut();
+        n_mut.prev = Some(prev.clone());
+        n_mut.next = Some(next.clone());
+        drop(n_mut);
+    }
+}
+
+pub fn print_nodes(nodes: &Vec<Rc<RefCell<Node>>>) {
+    let mut curr = nodes.iter().find(|n| n.borrow().val == 0).unwrap().clone();
+    loop {
+        print!("{}, ", curr.borrow().val);
+
+        let next = curr.borrow().next.as_ref().unwrap().clone();
+        curr = next;
+        if curr.borrow().val == 0 {
+            break;
+        }
+    }
+    print!("\n");
+}
+
+pub fn calc_coordinates(nodes: &Vec<Rc<RefCell<Node>>>) -> isize {
+    let zero = nodes.iter().find(|n| n.borrow().val == 0).unwrap();
+    let first = get_next(zero, 1000).borrow().val;
+    let second = get_next(zero, 2000).borrow().val;
+    let third = get_next(zero, 3000).borrow().val;
+
+    first + second + third
+}

src/lib.rs

@@ -10,6 +10,7 @@ pub mod day17;
 pub mod day18;
 pub mod day19;
 pub mod day2;
+pub mod day20;
 pub mod day3;
 pub mod day4;
 pub mod day5;