1 files changed, 101 insertions, 0 deletions
diff --git a/src/bin/day3.rs b/src/bin/day3.rs
new file mode 100644
index 0000000..53c77c9
--- /dev/null
+++ b/src/bin/day3.rs
@@ -0,0 +1,101 @@
+use std::collections::HashMap;
+
+static DAY: u8 = 3;
+
+fn main() {
+    let input = advent::read_lines(DAY);
+    println!("{DAY}a: {}", part_sum(&input));
+    println!("{DAY}b: {}", 0);
+}
+
+#[derive(Eq, PartialEq, Hash)]
+struct Position {
+    x: isize,
+    y: isize,
+}
+
+struct Schematics {
+    map: HashMap<Position, char>,
+}
+
+impl Schematics {
+    fn new(input: &[String]) -> Schematics {
+        let mut map = HashMap::new();
+        for (y, line) in input.iter().enumerate() {
+            for (x, c) in line.chars().enumerate() {
+                if c != '.' {
+                    map.insert(Position { x: x as isize, y: y as isize }, c);
+                }
+            }
+        }
+        Schematics { map }
+    }
+
+    fn has_neighboring_part(&self, pos: &Position) -> bool {
+        for y in -1 ..= 1 {
+            for x in -1 ..= 1 {
+                if let Some(obj) = self.map.get(&Position { x: pos.x + x, y: pos.y + y }) {
+                    if !obj.is_ascii_digit() {
+                        return true;
+                    }
+                }
+            }
+        }
+        false
+    }
+}
+
+fn part_sum(input: &[String]) -> u32 {
+    let schematics = Schematics::new(input);
+    let mut part_numbers = Vec::new();
+
+    for (y, line) in input.iter().enumerate() {
+        let mut number = 0;
+        let mut is_part_number = false;
+        for (x, c) in line.chars().enumerate() {
+            if let Some(digit) = c.to_digit(10) {
+                number *= 10;
+                number += digit;
+                if schematics.has_neighboring_part(&Position { x: x as isize, y: y as isize }) {
+                    is_part_number = true;
+                }
+            } else if number > 0 {
+                /* number ended within a line */
+                if is_part_number {
+                    part_numbers.push(number);
+                }
+                number = 0;
+                is_part_number = false;
+            }
+        }
+        if number > 0 && is_part_number {
+            /* number ended at the end of line */
+            part_numbers.push(number);
+        }
+    }
+
+    part_numbers.iter()
+                .sum()
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test() {
+        let input = [
+            "467..114..",
+            "...*......",
+            "..35..633.",
+            "......#...",
+            "617*......",
+            ".....+.58.",
+            "..592.....",
+            "......755.",
+            "...$.*....",
+            ".664.598..",
+        ].iter().map(|&x| String::from(x)).collect::<Vec<_>>();
+        assert_eq!(part_sum(&input), 4361);
+    }
+}