2024: Add solution for Day 3

Author: dcoles

2024/Cargo.lock

@@ -12,7 +12,7 @@ cargo run --bin day01
 
 1. [Historian Hysteria](day01) 🌟🌟
 2. [Red-Nosed Reports](day02) 🌟🌟
-3. [](day03)
+3. [Mull It Over](day03) 🌟🌟
 4. [](day04)
 5. [](day05)
 6. [](day06)

2024/README.md

@@ -6,3 +6,4 @@ edition = "2021"
 # See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
 
 [dependencies]
+regex = "1.11.1"

2024/day03/Cargo.toml

@@ -0,0 +1 @@
+xmul(2,4)%&mul[3,7]!@^do_not_mul(5,5)+mul(32,64]then(mul(11,8)mul(8,5))

2024/day03/example1.txt

@@ -0,0 +1 @@
+xmul(2,4)&mul[3,7]!^don't()_mul(5,5)+mul(32,64](mul(11,8)undo()?mul(8,5))

2024/day03/example2.txt

@@ -3,11 +3,10 @@
 
 use std::{fs, io};
 use std::path::Path;
+use regex::Regex;
 
 fn main() {
     let input = Input::from_file(format!("{}/input.txt", env!("CARGO_MANIFEST_DIR"))).expect("failed to read input");
-    //let input = Input::from_file(format!("{}/example1.txt", env!("CARGO_MANIFEST_DIR"))).expect("failed to read input");
-    println!("{input:?}");
 
     // Part 1
     println!("Part 1: {}", part1(&input));
@@ -17,24 +16,52 @@ fn main() {
 }
 
 fn part1(input: &Input) -> usize {
-    0
+    let mul_re = Regex::new(r"mul\((\d{1,3}),(\d{1,3})\)").unwrap();
+
+    mul_re.captures_iter(&input.input)
+        .map(|m| {
+            let a: usize = m.get(1).and_then(|m| m.as_str().parse().ok()).unwrap();
+            let b: usize = m.get(2).and_then(|m| m.as_str().parse().ok()).unwrap();
+
+            a * b
+        })
+        .sum()
 }
 
 fn part2(input: &Input) -> usize {
-    0
+    let instr_re = Regex::new(r"(?x) (?<instr>mul|do(n't)?) \( (?:(?<a>\d{1,3}) , (?<b>\d{1,3}))? \)").unwrap();
+
+    let mut is_do = true;
+    instr_re.captures_iter(&input.input)
+        .filter_map(|m| {
+            match m.name("instr").unwrap().as_str() {
+                "mul" => {
+                    let a: usize = m.name("a").and_then(|m| m.as_str().parse().ok()).unwrap();
+                    let b: usize = m.name("b").and_then(|m| m.as_str().parse().ok()).unwrap();
+
+                    if is_do {
+                        return Some(a * b)
+                    };
+                },
+                "do" => is_do = true,
+                "don't" => is_do = false,
+                instr => panic!("unknown instruction {instr:?}"),
+            }
+
+            None
+        }).sum()
 }
 
 #[derive(Debug, Clone)]
 struct Input {
-    values: Vec<String>,
+    input: String,
 }
 
 impl Input {
     fn from_file(path: impl AsRef<Path>) -> io::Result<Self> {
         let input = fs::read_to_string(path)?;
-        let values = input.lines().map(str::to_string).collect();
 
-        Ok(Self { values })
+        Ok(Self { input })
     }
 }
 
@@ -46,27 +73,27 @@ mod test {
     fn test_part1() {
         let input = Input::from_file("example1.txt").unwrap();
 
-        assert_eq!(part1(&input), 0);
+        assert_eq!(part1(&input), 161);
     }
 
     #[test]
     fn test_part1_solution() {
         let input = Input::from_file("input.txt").unwrap();
 
-        assert_eq!(part1(&input), 0);
+        assert_eq!(part1(&input), 175615763);
     }
 
     #[test]
     fn test_part2() {
-        let input = Input::from_file("example1.txt").unwrap();
+        let input = Input::from_file("example2.txt").unwrap();
 
-        assert_eq!(part2(&input), 0);
+        assert_eq!(part2(&input), 48);
     }
 
     #[test]
     fn test_part2_solution() {
         let input = Input::from_file("input.txt").unwrap();
 
-        assert_eq!(part2(&input), 0);
+        assert_eq!(part2(&input), 74361272);
     }
 }

2024/day03/input.txt

@@ -7,7 +7,7 @@ These are mostly written in [Rust](https://www.rust-lang.org/).
 I can also be found on BlueSky: [@dcoles.net](https://bsky.app/profile/dcoles.net)
 
 ## Solutions
-- [Advent of Code 2024](2024#readme): 4🌟
+- [Advent of Code 2024](2024#readme): 6🌟
 - [Advent of Code 2023](2023#readme): 45🌟
 - [Advent of Code 2022](2022#readme): 50🌟!
 - [Advent of Code 2021](2021#readme): 50🌟!