From 44396ade0adbb061dc948f1eb7be84149f6ab230 Mon Sep 17 00:00:00 2001
From: Jonni Liljamo <jonni@liljamo.com>
Date: Wed, 3 Dec 2025 13:12:35 +0200
Subject: [PATCH] feat: day3 part one

---
 Cargo.lock              |  7 +++++
 Cargo.toml              |  2 +-
 crates/day3/Cargo.toml  |  7 +++++
 crates/day3/src/main.rs | 65 +++++++++++++++++++++++++++++++++++++++++
 4 files changed, 80 insertions(+), 1 deletion(-)
 create mode 100644 crates/day3/Cargo.toml
 create mode 100644 crates/day3/src/main.rs

diff --git a/Cargo.lock b/Cargo.lock
index f6578a0..db74037 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -23,6 +23,13 @@ dependencies = [
  "common",
 ]
 
+[[package]]
+name = "day3"
+version = "0.1.0"
+dependencies = [
+ "common",
+]
+
 [[package]]
 name = "sc"
 version = "0.2.7"
diff --git a/Cargo.toml b/Cargo.toml
index f2246d7..3bba91c 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -1,3 +1,3 @@
 [workspace]
 resolver = "3"
-members = ["crates/common", "crates/day1", "crates/day2"]
+members = ["crates/common", "crates/day1", "crates/day2", "crates/day3"]
diff --git a/crates/day3/Cargo.toml b/crates/day3/Cargo.toml
new file mode 100644
index 0000000..22def1f
--- /dev/null
+++ b/crates/day3/Cargo.toml
@@ -0,0 +1,7 @@
+[package]
+name = "day3"
+version = "0.1.0"
+edition = "2024"
+
+[dependencies]
+common = { path = "../common" }
diff --git a/crates/day3/src/main.rs b/crates/day3/src/main.rs
new file mode 100644
index 0000000..d3bbe94
--- /dev/null
+++ b/crates/day3/src/main.rs
@@ -0,0 +1,65 @@
+#![no_std]
+
+use core::fmt::Write;
+
+use common::{print, read};
+
+fn main() {
+    let buf = [0u8; 65000];
+    read(buf.as_ptr(), buf.len());
+    let mut input = str::from_utf8(&buf).unwrap();
+    input = input.trim_end_matches(char::MIN);
+    input = input.trim();
+    let result_one = one(input);
+    let result_two = two(input);
+    print!(64, "one: {}\ntwo: {}\n", result_one, result_two);
+}
+
+fn one(input: &str) -> usize {
+    input
+        .split("\n")
+        .map(|bank| {
+            let mut first = char::MIN;
+            let mut first_index = 0;
+            let mut second = char::MIN;
+            let mut second_index = 0;
+
+            for (i, c) in bank.chars().enumerate() {
+                if c > first && i != bank.len() - 1 {
+                    first = c;
+                    first_index = i;
+
+                    second = char::MIN;
+                    second_index = 0;
+                } else if c > second && i > first_index {
+                    second = c;
+                    second_index = i;
+                }
+            }
+
+            let a = &bank[first_index..first_index + 1];
+            let b = &bank[second_index..second_index + 1];
+
+            let mut buf = [0; 2];
+            let c = common::format_str(&mut buf, format_args!("{}{}", a, b));
+
+            c.parse::<usize>().unwrap()
+        })
+        .sum::<usize>()
+}
+
+#[cfg(test)]
+mod test {
+    use super::*;
+
+    const EXAMPLE_INPUT: &str = r#"987654321111111
+811111111111119
+234234234234278
+818181911112111"#;
+
+    #[test]
+    fn example() {
+        assert_eq!(one(EXAMPLE_INPUT), 357);
+        assert_eq!(two(EXAMPLE_INPUT), 3121910778619);
+    }
+}
-- 
2.44.1