From 98559e201024df8d7625371c40956dcb0e80f7b6 Mon Sep 17 00:00:00 2001
From: Bert Peters <bert@bertptrs.nl>
Date: Fri, 1 Dec 2023 10:19:55 +0100
Subject: [PATCH] Day 1 2023 part 1

---
 2023/src/day01.rs | 50 ++++++++++++++++++++++++++++++++++++++++++++---
 1 file changed, 47 insertions(+), 3 deletions(-)

diff --git a/2023/src/day01.rs b/2023/src/day01.rs
index 7c1760f..f783805 100644
--- a/2023/src/day01.rs
+++ b/2023/src/day01.rs
@@ -1,7 +1,51 @@
-pub fn part1(_input: &[u8]) -> anyhow::Result<String> {
+use anyhow::Result;
+
+fn to_digit(c: u8) -> Option<u32> {
+    match c {
+        b'0'..=b'9' => Some(u32::from(c - b'0')),
+        _ => None,
+    }
+}
+
+pub fn part1(input: &[u8]) -> Result<String> {
+    let mut it = input.iter();
+    let mut sum = 0;
+
+    loop {
+        let mut first = None;
+        let mut last = 0;
+
+        for digit in it
+            .by_ref()
+            .take_while(|&&c| c != b'\n')
+            .filter_map(|&c| to_digit(c))
+        {
+            first.get_or_insert(digit);
+            last = digit;
+        }
+
+        if let Some(first) = first {
+            sum += 10 * first + last;
+        } else {
+            break;
+        }
+    }
+
+    Ok(sum.to_string())
+}
+
+pub fn part2(_input: &[u8]) -> Result<String> {
     anyhow::bail!("Not implemented")
 }
 
-pub fn part2(_input: &[u8]) -> anyhow::Result<String> {
-    anyhow::bail!("Not implemented")
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    const SAMPLE: &[u8] = include_bytes!("samples/01.txt");
+
+    #[test]
+    fn sample_part1() {
+        assert_eq!("142", part1(SAMPLE).unwrap());
+    }
 }