day15: problem 1 & 2 solutions

15/Cargo.lock

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+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+version = 3
+
+[[package]]
+name = "day15"
+version = "0.1.0"

15/Cargo.toml

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+[package]
+name = "day15"
+version = "0.1.0"
+edition = "2021"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]

15/src/main.rs

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+use std::collections::HashMap;
+use std::fs::File;
+use std::io::{BufRead, BufReader, Lines};
+use std::time::{Duration, Instant};
+
+// BOILERPLATE
+type InputIter = Lines<BufReader<File>>;
+
+fn get_input() -> InputIter {
+    let f = File::open("input").unwrap();
+    let br = BufReader::new(f);
+    br.lines()
+}
+
+fn main() {
+    let start = Instant::now();
+    let ans1 = problem1(get_input());
+    let duration = start.elapsed();
+    println!("Problem 1 solution: {} [{}s]", ans1, duration.as_secs_f64());
+
+    let start = Instant::now();
+    let ans2 = problem2(get_input());
+    let duration = start.elapsed();
+    println!("Problem 2 solution: {} [{}s]", ans2, duration.as_secs_f64());
+}
+
+// COMMON
+
+fn hash_string(s: &str) -> u64 {
+    let mut val = 0u64;
+    for c in s.bytes() {
+        val += c as u64;
+        val *= 17;
+        val %= 256;
+    }
+    val
+}
+
+// PROBLEM 1 solution
+
+fn problem1<T: BufRead>(mut input: Lines<T>) -> u64 {
+    let line = input.next().unwrap().unwrap();
+    line.split(',').map(|s| hash_string(s)).sum()
+}
+
+// PROBLEM 2 solution
+
+#[derive(Clone, Default)]
+struct LensBox {
+    // lenses k: lens label v: focal length
+    lenses: HashMap<String, u8>,
+    // order is the lens stack, values are labels into lenses
+    order: Vec<String>,
+}
+
+impl LensBox {
+    fn add_lens(&mut self, label: &str, focal_length: u8) {
+        // If there is not already a lens in the box with the same label, add
+        // the lens to the box immediately behind any lenses already in the box.
+        // Don't move any of the other lenses when you do this. If there aren't
+        // any lenses in the box, the new lens goes all the way to the front of
+        // the box.
+        if self.lenses.insert(label.to_owned(), focal_length).is_none() {
+            self.order.push(label.to_owned());
+        }
+    }
+    //If the operation character is a dash (-), go to the relevant box and
+    //remove the lens with the given label if it is present in the box. Then,
+    //move any remaining lenses as far forward in the box as they can go without
+    //changing their order, filling any space made by removing the indicated
+    //lens. (If no lens in that box has the given label, nothing happens.)
+    fn remove_lens_if_present(&mut self, label: &str) {
+        if let Some(_) = self.lenses.remove(label) {
+            self.order.remove(
+                self.order
+                    .iter()
+                    .position(|s| s == label)
+                    .expect("We had the lens in lenses but not in order?!"),
+            );
+        }
+    }
+
+    fn total_lens_power(&self) -> u64{
+        self.order.iter().enumerate().map(|(lens_idx, label)| (lens_idx+1) as u64 * self.lenses[label] as u64).sum()
+    }
+}
+
+enum Instruction {
+    Replace(String, u8),
+    Remove(String),
+}
+
+impl From<&str> for Instruction {
+    fn from(s: &str) -> Self {
+        let op_pos = s.find(|c| c == '-' || c == '=').expect("No operation?!");
+        let op = s.chars().nth(op_pos).unwrap();
+        let (label, op_focal) = s.split_once(|c| c == '-' || c == '=').unwrap();
+
+        match op {
+            '-' => Self::Remove(label.to_owned()),
+            '=' => Self::Replace(label.to_owned(), op_focal.parse().unwrap()),
+            _ => panic!("unexpected op {}", op),
+        }
+    }
+}
+
+impl Instruction {
+    fn execute(&self, boxes: &mut [LensBox; 256]) {
+        match self {
+            Self::Remove(label) => boxes[hash_string(label) as usize].remove_lens_if_present(label),
+            Self::Replace(label, focal) => {
+                boxes[hash_string(label) as usize].add_lens(label, *focal)
+            }
+        }
+    }
+}
+
+fn print_boxes(boxes: &[LensBox; 256]) {
+    for (idx, b) in boxes.iter().enumerate() {
+        if !b.order.is_empty() {
+            print!("Box {}:", idx);
+            for label in &b.order {
+                print!(" [{} {}]", label, b.lenses[label]);
+            }
+            println!();
+        }
+    }
+}
+
+fn problem2<T: BufRead>(mut input: Lines<T>) -> u64 {
+    let line = input.next().unwrap().unwrap();
+
+    let instructions: Vec<_> = line.split(',').map(|s| Instruction::from(s)).collect();
+    let mut boxes: [LensBox; 256] = std::array::from_fn(|_| LensBox::default());
+
+    for inst in instructions {
+        inst.execute(&mut boxes);
+    }
+
+    boxes.iter().enumerate().map(|(box_idx, b)| (box_idx + 1) as u64 * b.total_lens_power()).sum()
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::*;
+    use std::io::Cursor;
+
+    const EXAMPLE: &str = &"rn=1,cm-,qp=3,cm=2,qp-,pc=4,ot=9,ab=5,pc-,pc=6,ot=7";
+
+    #[test]
+    fn problem1_test_hash() {
+        assert_eq!(hash_string(&"HASH"), 52);
+    }
+    #[test]
+    fn problem1_example() {
+        let c = Cursor::new(EXAMPLE);
+        assert_eq!(problem1(c.lines()), 1320);
+    }
+
+    #[test]
+    fn problem2_example() {
+        let c = Cursor::new(EXAMPLE);
+        assert_eq!(problem2(c.lines()), 145);
+    }
+}