day3 part 1

2023/day3/src/main.rs

@@ -0,0 +1,83 @@
+fn main() {
+    let kind = std::env::args().nth(1).unwrap_or("naive".into());
+
+    let input = std::hint::black_box(include_str!("../input.txt")).to_owned();
+
+    let result = match kind.as_str() {
+        "part1" => part1(&input),
+        "part2" => part2(&input),
+        _ => {
+            eprintln!("error: invalid mode, must be part1");
+            std::process::exit(1);
+        }
+    };
+
+    println!("result: {result}");
+}
+
+fn part1(input: &str) -> u64 {
+    fn contains_symbol(s: &str) -> bool {
+        s.chars().any(|c| !c.is_ascii_digit() && c != '.')
+    }
+
+    let len = input.lines().next().unwrap().len();
+    let empty_border = std::iter::repeat('.').take(len).collect::<String>();
+
+    let mut prev2 = empty_border.as_str();
+    let mut prev1 = input.lines().next().unwrap();
+
+    let mut acc = 0;
+
+    for next in input.lines().skip(1).chain(Some(empty_border.as_str())) {
+        let mut numbers = prev1.char_indices().peekable();
+        while let Some((start, c)) = numbers.next() {
+            if c.is_ascii_digit() {
+                let mut end = start;
+                while let Some((idx, '0'..='9')) = numbers.next() {
+                    end = idx;
+                }
+
+                let box_bounds = (start.saturating_sub(1))..std::cmp::min(end + 2, len);
+                let number = prev1[start..=end].parse::<u64>().unwrap();
+
+                if contains_symbol(&prev2[box_bounds.clone()])
+                    || contains_symbol(&prev1[box_bounds.clone()])
+                    || contains_symbol(&next[box_bounds])
+                {
+                    acc += number;
+                }
+            }
+        }
+
+        prev2 = prev1;
+        prev1 = next;
+    }
+
+    acc
+}
+
+fn part2(input: &str) -> u64 {
+    0
+}
+
+#[cfg(test)]
+mod tests {
+    #[test]
+    fn part1_small() {
+        assert_eq!(super::part1(include_str!("../input_small.txt")), 8);
+    }
+
+    #[test]
+    fn part1() {
+        assert_eq!(super::part1(include_str!("../input.txt")), 1931);
+    }
+
+    #[test]
+    fn part2_small() {
+        assert_eq!(super::part2(include_str!("../input_small.txt")), 2286);
+    }
+    #[test]
+    fn part2() {
+        assert_eq!(super::part2(include_str!("../input.txt")), 83105);
+    }
+}