solve: day3

Author: tom-anders

Cargo.toml

@@ -2,7 +2,7 @@
 resolver = "2"
 members = [
     "aoc_lib/aoc_derive",
-    "aoc_lib/utils", "day1", "day2",
+    "aoc_lib/utils", "day1", "day2", "day3",
 ]
 
 [workspace.dependencies]

day3/Cargo.toml

@@ -0,0 +1,18 @@
+[package]
+name = "day3"
+version = "0.1.0"
+edition = "2024"
+
+[dependencies]
+aoc_derive.path = '../aoc_lib/aoc_derive'
+utils.path = '../aoc_lib/utils'
+derive_more.workspace = true
+itertools.workspace = true
+lazy-regex.workspace = true
+parse-display.workspace = true
+rayon.workspace = true
+regex.workspace = true
+num.workspace = true
+
+[dev-dependencies]
+pretty_assertions.workspace = true

day3/src/main.rs

@@ -0,0 +1,64 @@
+use aoc_derive::aoc_main;
+use itertools::Itertools;
+use utils::*;
+
+fn find_best(numbers: &[usize], cur: usize, depth: u32, max: usize) -> Option<usize> {
+    if depth == 12 {
+        return Some(cur);
+    }
+
+    if numbers.is_empty() || cur + 10_usize.pow(12 - depth) < max {
+        return None;
+    }
+
+    let skip_result = find_best(&numbers[1..], cur, depth, max);
+
+    let no_skip_result = find_best(
+        &numbers[1..],
+        cur + 10_usize.pow(12 - depth - 1) * numbers[0],
+        depth + 1,
+        skip_result.unwrap_or(max),
+    );
+
+    skip_result.max(no_skip_result)
+}
+
+#[aoc_main]
+fn solve(input: Input) -> impl Into<Solution> {
+    let banks = input
+        .lines()
+        .map(|line| line.chars().map(|c| c.to_digit(10).unwrap() as usize).collect_vec())
+        .collect_vec();
+
+    let part1 = banks
+        .iter()
+        .map(|bank| {
+            bank.iter()
+                .enumerate()
+                .flat_map(|(i, n1)| bank.iter().skip(i + 1).map(move |n2| 10 * n1 + n2))
+                .max()
+                .unwrap()
+        })
+        .sum_usize();
+
+    let part2 = banks.iter().map(|bank| find_best(bank, 0, 0, 0).unwrap()).sum_usize();
+
+    (part1, part2)
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    #[test]
+    fn test_examples() {
+        use utils::assert_example;
+        assert_example!(
+            r#"987654321111111
+811111111111119
+234234234234278
+818181911112111"#,
+            357,
+            3121910778619_usize
+        );
+    }
+}